PR symtab/11942

	PR symtab/11942
	* dwarf2read.c (dwarf2_per_objfile): New members debug_info_type_hash,
	debug_types_type_hash.
	(dwarf2_cu, dwarf2_per_cu_data): Delete member type_hash.
	All uses updated.
	(lookup_die_type): Renamed from tag_type_to_tag.  First look in
	appropriate type_hash table.  All callers updated.
	(allocate_signatured_type_table): Renamed from
	allocate_signatured_type_hash_table.  All callers updated.
	(create_signatured_type_table_from_index): Renamed from
	create_signatured_type_hash_from_index.  All callers updated.
	(read_die_type): Add comment.  Move actual reading to ...
	(read_die_type_1): ... here.  New function.
	(follow_die_ref_or_sig): Tweak comment.
	(set_die_type): Rewrite to use appropriate choice of
	debug_info_type_hash or debug_types_type_hash.
	(get_die_type_at_offset): New function.
	(get_die_type): Call it.

	testsuite/
	PR symtab/11942
	* gdb.dwarf2/dw4-sig-types.cc: New file.
	* gdb.dwarf2/dw4-sig-types.h: New file.
	* gdb.dwarf2/dw4-sig-types-b.cc: New file.
	* gdb.dwarf2/dw4-sig-types.exp: New file.