This removes the ALL_OBJSECTIONS macro, replacing its uses with ranged
for loops.

The special code in this macro for noticing a "break" from the inner
loop was only needed in a single place; so rather than try to
replicate this, I've simply replaced that use with a "goto".

gdb/ChangeLog
2019-01-09  Tom Tromey  <tom@tromey.com>

	* symfile.c (overlay_invalidate_all, find_pc_overlay)
	(find_pc_mapped_section, list_overlays_command)
	(map_overlay_command, unmap_overlay_command)
	(simple_overlay_update): Use all_objfiles.
	* spu-tdep.c (spu_overlay_update): Use all_objfiles.
	* printcmd.c (info_symbol_command): Use all_objfiles.
	* objfiles.h (ALL_OBJSECTIONS): Remove.
	* maint.c (maintenance_translate_address): Use all_objfiles.
	* gcore.c (gcore_create_callback): Use all_objfiles.
	(objfile_find_memory_regions): Likewise.