This patch starts from the desire to eliminate
make_cleanup_ui_file_delete, but then goes beyond.  It makes ui_file &
friends a real C++ class hierarchy, and switches temporary
ui_file-like objects to stack-based allocation.

- mem_fileopen -> string_file

mem_fileopen is replaced with a new string_file class that is treated
as a value class created on the stack.  This alone eliminates most
make_cleanup_ui_file_delete calls, and, simplifies code a whole lot
(diffstat shows around 1k loc dropped.)

string_file's internal buffer is a std::string, thus the "string" in
the name.  This simplifies the implementation much, compared to
mem_fileopen, which managed growing its internal buffer manually.

- ui_file_as_string, ui_file_strdup, ui_file_obsavestring all gone

The new string_file class has a string() method that provides direct
writable access to the internal std::string buffer.  This replaced
ui_file_as_string, which forced a copy of the same data the stream had
inside.  With direct access via a writable reference, we can instead
move the string out of the string_stream, avoiding deep string
copying.

Related, ui_file_xstrdup calls are replaced with xstrdup'ping the
stream's string, and ui_file_obsavestring is replaced by
obstack_copy0.

With all those out of the way, getting rid of the weird ui_file_put
mechanism was possible.

- New ui_file::printf, ui_file::puts, etc. methods

These simplify / clarify client code.  I considered splitting
client-code changes, like these, e.g.:

  -  stb = mem_fileopen ();
  -  fprintf_unfiltered (stb, "%s%s%s",
  -		      _("The valid values are:\n"),
  -		      regdesc,
  -		      _("The default is \"std\"."));
  +  string_file stb;
  +  stb.printf ("%s%s%s",
  +	      _("The valid values are:\n"),
  +	      regdesc,
  +	      _("The default is \"std\"."));

In two steps, with the first step leaving fprintf_unfiltered (etc.)
calls in place, and only afterwards do a pass to change all those to
call stb.printf etc..  I didn't do that split, because (when I tried),
it turned out to be pointless make-work: the first pass would have to
touch the fprintf_unfiltered line anyway, to replace "stb" with
"&stb".

- gdb_fopen replaced with stack-based objects

This avoids the need for cleanups or unique_ptr's.  I.e., this:

      struct ui_file *file = gdb_fopen (filename, "w");
      if (filename == NULL)
 	perror_with_name (filename);
      cleanups = make_cleanup_ui_file_delete (file);
      // use file.
      do_cleanups (cleanups);

is replaced with this:

      stdio_file file;
      if (!file.open (filename, "w"))
 	perror_with_name (filename);
      // use file.

- odd contorsions in null_file_write / null_file_fputs around when to
  call to_fputs / to_write eliminated.

- Global null_stream object

A few places that were allocating a ui_file in order to print to
"nowhere" are adjusted to instead refer to a new 'null_stream' global
stream.

- TUI's tui_sfileopen eliminated.  TUI's ui_file much simplified

The TUI's ui_file was serving a dual purpose.  It supported being used
as string buffer, and supported being backed by a stdio FILE.  The
string buffer part is gone, replaced by using of string_file.  The
'FILE *' support is now much simplified, by making the TUI's ui_file
inherit from stdio_file.

gdb/ChangeLog:
2017-02-02  Pedro Alves  <palves@redhat.com>

	* ada-lang.c (type_as_string): Use string_file.
	* ada-valprint.c (ada_print_floating): Use string_file.
	* ada-varobj.c (ada_varobj_scalar_image)
	(ada_varobj_get_value_image): Use string_file.
	* aix-thread.c (aix_thread_extra_thread_info): Use string_file.
	* arm-tdep.c (_initialize_arm_tdep): Use string_printf.
	* breakpoint.c (update_inserted_breakpoint_locations)
	(insert_breakpoint_locations, reattach_breakpoints)
	(print_breakpoint_location, print_one_detail_ranged_breakpoint)
	(print_it_watchpoint): Use string_file.
	(save_breakpoints): Use stdio_file.
	* c-exp.y (oper): Use string_file.
	* cli/cli-logging.c (set_logging_redirect): Use ui_file_up and
	tee_file.
	(pop_output_files): Use delete.
	(handle_redirections): Use stdio_file and tee_file.
	* cli/cli-setshow.c (do_show_command): Use string_file.
	* compile/compile-c-support.c (c_compute_program): Use
	string_file.
	* compile/compile-c-symbols.c (generate_vla_size): Take a
	'string_file &' instead of a 'ui_file *'.
	(generate_c_for_for_one_variable): Take a 'string_file &' instead
	of a 'ui_file *'.  Use string_file.
	(generate_c_for_variable_locations): Take a 'string_file &'
	instead of a 'ui_file *'.
	* compile/compile-internal.h (generate_c_for_for_one_variable):
	Take a 'string_file &' instead of a 'ui_file *'.
	* compile/compile-loc2c.c (push, pushf, unary, binary)
	(print_label, pushf_register_address, pushf_register)
	(do_compile_dwarf_expr_to_c): Take a 'string_file &' instead of a
	'ui_file *'.  Adjust.
	* compile/compile.c (compile_to_object): Use string_file.
	* compile/compile.h (compile_dwarf_expr_to_c)
	(compile_dwarf_bounds_to_c): Take a 'string_file &' instead of a
	'ui_file *'.
	* cp-support.c (inspect_type): Use string_file and obstack_copy0.
	(replace_typedefs_qualified_name): Use string_file and
	obstack_copy0.
	* disasm.c (gdb_pretty_print_insn): Use string_file.
	(gdb_disassembly): Adjust reference the null_stream global.
	(do_ui_file_delete): Delete.
	(gdb_insn_length): Use null_stream.
	* dummy-frame.c (maintenance_print_dummy_frames): Use stdio_file.
	* dwarf2loc.c (dwarf2_compile_property_to_c)
	(locexpr_generate_c_location, loclist_generate_c_location): Take a
	'string_file &' instead of a 'ui_file *'.
	* dwarf2loc.h (dwarf2_compile_property_to_c): Likewise.
	* dwarf2read.c (do_ui_file_peek_last): Delete.
	(dwarf2_compute_name): Use string_file.
	* event-top.c (gdb_setup_readline): Use stdio_file.
	* gdbarch.sh (verify_gdbarch): Use string_file.
	* gdbtypes.c (safe_parse_type): Use null_stream.
	* guile/scm-breakpoint.c (gdbscm_breakpoint_commands): Use
	string_file.
	* guile/scm-disasm.c (gdbscm_print_insn_from_port): Take a
	'string_file *' instead of a 'ui_file *'.
	(gdbscm_arch_disassemble): Use string_file.
	* guile/scm-frame.c (frscm_print_frame_smob): Use string_file.
	* guile/scm-ports.c (class ioscm_file_port): Now a class that
	inherits from ui_file.
	(ioscm_file_port_delete, ioscm_file_port_rewind)
	(ioscm_file_port_put): Delete.
	(ioscm_file_port_write): Rename to ...
	(ioscm_file_port::write): ... this.  Remove file_port_magic
	checks.
	(ioscm_file_port_new): Delete.
	(ioscm_with_output_to_port_worker): Use ioscm_file_port and
	ui_file_up.
	* guile/scm-type.c (tyscm_type_name): Use string_file.
	* guile/scm-value.c (vlscm_print_value_smob, gdbscm_value_print):
	Use string_file.
	* infcmd.c (print_return_value_1): Use string_file.
	* infrun.c (print_target_wait_results): Use string_file.
	* language.c (add_language): Use string_file.
	* location.c (explicit_to_string_internal): Use string_file.
	* main.c (captured_main_1): Use null_file.
	* maint.c (maintenance_print_architecture): Use stdio_file.
	* mi/mi-cmd-stack.c (list_arg_or_local): Use string_file.
	* mi/mi-common.h (struct mi_interp) <out, err, log, targ,
	event_channel>: Change type to mi_console_file pointer.
	* mi/mi-console.c (mi_console_file_fputs, mi_console_file_flush)
	(mi_console_file_delete): Delete.
	(struct mi_console_file): Delete.
	(mi_console_file_magic): Delete.
	(mi_console_file_new): Delete.
	(mi_console_file::mi_console_file): New.
	(mi_console_file_delete): Delete.
	(mi_console_file_fputs): Delete.
	(mi_console_file::write): New.
	(mi_console_raw_packet): Delete.
	(mi_console_file::flush): New.
	(mi_console_file_flush): Delete.
	(mi_console_set_raw): Rename to ...
	(mi_console_file::set_raw): ... this.
	* mi/mi-console.h (class mi_console_file): New class.
	(mi_console_file_new, mi_console_set_raw): Delete.
	* mi/mi-interp.c (mi_interpreter_init): Use mi_console_file.
	(mi_set_logging): Use delete and tee_file.  Adjust.
	* mi/mi-main.c (output_register): Use string_file.
	(mi_cmd_data_evaluate_expression): Use string_file.
	(mi_cmd_data_read_memory): Use string_file.
	(mi_cmd_execute, print_variable_or_computed): Use string_file.
	* mi/mi-out.c (mi_ui_out::main_stream): New.
	(mi_ui_out::rewind): Use main_stream and
	string_file.
	(mi_ui_out::put): Use main_stream and string_file.
	(mi_ui_out::mi_ui_out): Remove 'stream' parameter.
	Allocate a 'string_file' instead.
	(mi_out_new): Don't allocate a mem_fileopen stream here.
	* mi/mi-out.h (mi_ui_out::mi_ui_out): Remove 'stream' parameter.
	(mi_ui_out::main_stream): Declare method.
	* printcmd.c (eval_command): Use string_file.
	* psymtab.c (maintenance_print_psymbols): Use stdio_file.
	* python/py-arch.c (archpy_disassemble): Use string_file.
	* python/py-breakpoint.c (bppy_get_commands): Use string_file.
	* python/py-frame.c (frapy_str): Use string_file.
	* python/py-framefilter.c (py_print_type, py_print_single_arg):
	Use string_file.
	* python/py-type.c (typy_str): Use string_file.
	* python/py-unwind.c (unwind_infopy_str): Use string_file.
	* python/py-value.c (valpy_str): Use string_file.
	* record-btrace.c (btrace_insn_history): Use string_file.
	* regcache.c (regcache_print): Use stdio_file.
	* reggroups.c (maintenance_print_reggroups): Use stdio_file.
	* remote.c (escape_buffer): Use string_file.
	* rust-lang.c (rust_get_disr_info): Use string_file.
	* serial.c (serial_open_ops_1): Use stdio_file.
	(do_serial_close): Use delete.
	* stack.c (print_frame_arg): Use string_file.
	(print_frame_args): Remove local mem_fileopen stream, not used.
	(print_frame): Use string_file.
	* symmisc.c (maintenance_print_symbols): Use stdio_file.
	* symtab.h (struct symbol_computed_ops) <generate_c_location>:
	Take a 'string_file *' instead of a 'ui_file *'.
	* top.c (new_ui): Use stdio_file and stderr_file.
	(free_ui): Use delete.
	(execute_command_to_string): Use string_file.
	(quit_confirm): Use string_file.
	* tracepoint.c (collection_list::append_exp): Use string_file.
	* tui/tui-disasm.c (tui_disassemble): Use string_file.
	* tui/tui-file.c: Don't include "ui-file.h".
	(enum streamtype, struct tui_stream): Delete.
	(tui_file_new, tui_file_delete, tui_fileopen, tui_sfileopen)
	(tui_file_isatty, tui_file_rewind, tui_file_put): Delete.
	(tui_file::tui_file): New method.
	(tui_file_fputs): Delete.
	(tui_file_get_strbuf): Delete.
	(tui_file::puts): New method.
	(tui_file_adjust_strbuf): Delete.
	(tui_file_flush): Delete.
	(tui_file::flush): New method.
	* tui/tui-file.h: Tweak intro comment.
	Include ui-file.h.
	(tui_fileopen, tui_sfileopen, tui_file_get_strbuf)
	(tui_file_adjust_strbuf): Delete declarations.
	(class tui_file): New class.
	* tui/tui-io.c (tui_initialize_io): Use tui_file.
	* tui/tui-regs.c (tui_restore_gdbout): Use delete.
	(tui_register_format): Use string_stream.
	* tui/tui-stack.c (tui_make_status_line): Use string_file.
	(tui_get_function_from_frame): Use string_file.
	* typeprint.c (type_to_string): Use string_file.
	* ui-file.c (struct ui_file, ui_file_magic, ui_file_new): Delete.
	(null_stream): New global.
	(ui_file_delete): Delete.
	(ui_file::ui_file): New.
	(null_file_isatty): Delete.
	(ui_file::~ui_file): New.
	(null_file_rewind): Delete.
	(ui_file::printf): New.
	(null_file_put): Delete.
	(null_file_flush): Delete.
	(ui_file::putstr): New.
	(null_file_write): Delete.
	(ui_file::putstrn): New.
	(null_file_read): Delete.
	(ui_file::putc): New.
	(null_file_fputs): Delete.
	(null_file_write_async_safe): Delete.
	(ui_file::vprintf): New.
	(null_file_delete): Delete.
	(null_file::write): New.
	(null_file_fseek): Delete.
	(null_file::puts): New.
	(ui_file_data): Delete.
	(null_file::write_async_safe): New.
	(gdb_flush, ui_file_isatty): Adjust.
	(ui_file_put, ui_file_rewind): Delete.
	(ui_file_write): Adjust.
	(ui_file_write_for_put): Delete.
	(ui_file_write_async_safe, ui_file_read): Adjust.
	(ui_file_fseek): Delete.
	(fputs_unfiltered): Adjust.
	(set_ui_file_flush, set_ui_file_isatty, set_ui_file_rewind)
	(set_ui_file_put, set_ui_file_write, set_ui_file_write_async_safe)
	(set_ui_file_read, set_ui_file_fputs, set_ui_file_fseek)
	(set_ui_file_data): Delete.
	(string_file::~string_file, string_file::write)
	(struct accumulated_ui_file, do_ui_file_xstrdup, ui_file_xstrdup)
	(do_ui_file_as_string, ui_file_as_string): Delete.
	(do_ui_file_obsavestring, ui_file_obsavestring): Delete.
	(struct mem_file): Delete.
	(mem_file_new): Delete.
	(stdio_file::stdio_file): New.
	(mem_file_delete): Delete.
	(stdio_file::stdio_file): New.
	(mem_fileopen): Delete.
	(stdio_file::~stdio_file): New.
	(mem_file_rewind): Delete.
	(stdio_file::set_stream): New.
	(mem_file_put): Delete.
	(stdio_file::open): New.
	(mem_file_write): Delete.
	(stdio_file_magic, struct stdio_file): Delete.
	(stdio_file_new, stdio_file_delete, stdio_file_flush): Delete.
	(stdio_file::flush): New.
	(stdio_file_read): Rename to ...
	(stdio_file::read): ... this.  Adjust.
	(stdio_file_write): Rename to ...
	(stdio_file::write): ... this.  Adjust.
	(stdio_file_write_async_safe): Rename to ...
	(stdio_file::write_async_safe) ... this.  Adjust.
	(stdio_file_fputs): Rename to ...
	(stdio_file::puts) ... this.  Adjust.
	(stdio_file_isatty): Delete.
	(stdio_file_fseek): Delete.
	(stdio_file::isatty): New.
	(stderr_file_write): Rename to ...
	(stderr_file::write) ... this.  Adjust.
	(stderr_file_fputs): Rename to ...
	(stderr_file::puts) ... this.  Adjust.
	(stderr_fileopen, stdio_fileopen, gdb_fopen): Delete.
	(stderr_file::stderr_file): New.
	(tee_file_magic): Delete.
	(struct tee_file): Delete.
	(tee_file::tee_file): New.
	(tee_file_new): Delete.
	(tee_file::~tee_file): New.
	(tee_file_delete): Delete.
	(tee_file_flush): Rename to ...
	(tee_file::flush): ... this.  Adjust.
	(tee_file_write): Rename to ...
	(tee_file::write): ... this.  Adjust.
	(tee_file::write_async_safe): New.
	(tee_file_fputs): Rename to ...
	(tee_file::puts): ... this.  Adjust.
	(tee_file_isatty): Rename to ...
	(tee_file::isatty): ... this.  Adjust.
	* ui-file.h (struct obstack, struct ui_file): Don't
	forward-declare.
	(ui_file_new, ui_file_flush_ftype, set_ui_file_flush)
	(ui_file_write_ftype)
	(set_ui_file_write, ui_file_fputs_ftype, set_ui_file_fputs)
	(ui_file_write_async_safe_ftype, set_ui_file_write_async_safe)
	(ui_file_read_ftype, set_ui_file_read, ui_file_isatty_ftype)
	(set_ui_file_isatty, ui_file_rewind_ftype, set_ui_file_rewind)
	(ui_file_put_method_ftype, ui_file_put_ftype, set_ui_file_put)
	(ui_file_delete_ftype, set_ui_file_data, ui_file_fseek_ftype)
	(set_ui_file_fseek): Delete.
	(ui_file_data, ui_file_delete, ui_file_rewind)
	(struct ui_file): New.
	(ui_file_up): New.
	(class null_file): New.
	(null_stream): Declare.
	(ui_file_write_for_put, ui_file_put): Delete.
	(ui_file_xstrdup, ui_file_as_string, ui_file_obsavestring):
	Delete.
	(ui_file_fseek, mem_fileopen, stdio_fileopen, stderr_fileopen)
	(gdb_fopen, tee_file_new): Delete.
	(struct string_file): New.
	(struct stdio_file): New.
	(stdio_file_up): New.
	(struct stderr_file): New.
	(class tee_file): New.
	* ui-out.c (ui_out::field_stream): Take a 'string_file &' instead
	of a 'ui_file *'.  Adjust.
	* ui-out.h (class ui_out) <field_stream>: Likewise.
	* utils.c (do_ui_file_delete, make_cleanup_ui_file_delete)
	(null_stream): Delete.
	(error_stream): Take a 'string_file &' instead of a 'ui_file *'.
	Adjust.
	* utils.h (struct ui_file): Delete forward declaration..
	(make_cleanup_ui_file_delete, null_stream): Delete declarations.
	(error_stream): Take a 'string_file &' instead of a
	'ui_file *'.
	* varobj.c (varobj_value_get_print_value): Use string_file.
	* xtensa-tdep.c (xtensa_verify_config): Use string_file.
	* gdbarch.c: Regenerate.