This fixes all the straightforward -Wshadow=local warnings in gdb.  A
few standard approaches are used here:

* Renaming an inner (or outer, but more commonly inner) variable;
* Lowering a declaration to avoid a clash;
* Moving a declaration into a more inner scope to avoid a clash,
  including the special case of moving a declaration into a loop header.

I did not consider any of the changes in this patch to be particularly
noteworthy, though of course they should all still be examined.

gdb/ChangeLog
2018-10-04  Tom Tromey  <tom@tromey.com>

	* ctf.c (SET_ARRAY_FIELD): Rename "u32".
	* p-valprint.c (pascal_val_print): Split inner "i" variable.
	* xtensa-tdep.c (xtensa_push_dummy_call): Declare "i" in loop
	header.
	* xstormy16-tdep.c (xstormy16_push_dummy_call): Declare "val" in
	more inner scope.
	* xcoffread.c (read_xcoff_symtab): Rename inner "symbol".
	* varobj.c (varobj_update): Rename inner "newobj",
	"type_changed".
	* valprint.c (generic_emit_char): Rename inner "buf".
	* valops.c (find_overload_match): Rename inner "temp".
	(value_struct_elt_for_reference): Declare "v" in more inner
	scope.
	* v850-tdep.c (v850_push_dummy_call): Rename "len".
	* unittests/array-view-selftests.c (run_tests): Rename inner
	"vec".
	* tui/tui-stack.c (tui_show_frame_info): Declare "i" in loop
	header.
	* tracepoint.c (merge_uploaded_trace_state_variables): Declare
	"tsv" in more inner scope.
	(print_one_static_tracepoint_marker): Rename inner
	"tuple_emitter".
	* tic6x-tdep.c (tic6x_analyze_prologue): Declare "inst" lower.
	(tic6x_push_dummy_call): Don't redeclare "addr".
	* target-float.c: Declare "dto" lower.
	* symtab.c (lookup_local_symbol): Rename inner "sym".
	(find_pc_sect_line): Rename inner "pc".
	* stack.c (print_frame): Don't redeclare "gdbarch".
	(return_command): Rename inner "gdbarch".
	* s390-tdep.c (s390_prologue_frame_unwind_cache): Renam inner
	"sp".
	* rust-lang.c (rust_internal_print_type): Declare "i" in loop
	header.
	* rs6000-tdep.c (ppc_process_record): Rename inner "addr".
	* riscv-tdep.c (riscv_push_dummy_call): Declare "info" in inner
	scope.
	* remote.c (remote_target::update_thread_list): Don't redeclare
	"tp".
	(remote_target::process_initial_stop_replies): Rename inner
	"thread".
	(remote_target::remote_parse_stop_reply): Don't redeclare "p".
	(remote_target::wait_as): Don't redeclare "stop_reply".
	(remote_target::get_thread_local_address): Rename inner
	"result".
	(remote_target::get_tib_address): Likewise.