Add Ada support for .debug_names

Add Ada support for .debug_names

This patch adds support for Ada to .debug_names.  I opted to leave
.gdb_index alone, because in my view it is a defunct format.

gdb/ChangeLog
2019-09-10  Tom Tromey  <tromey@adacore.com>

	* dwarf-index-write.c (write_psymbols): Extend error message.
	(debug_names::insert): Add Ada code.
	(debug_names::write_psymbols): Remove Ada check.
	(debug_names) <m_string_obstack>: New member.
	* dwarf2read.c (gdb_index_symbol_name_matcher): Remove.
	(gdb_index_symbol_name_matcher::matches): Remove.
	(mapped_index_base::find_name_components_bounds): Add "lang"
	parameter.
	(mapped_index_base::build_name_components): Also split names
	according to Ada syntax.
	(dw2_expand_symtabs_matching_symbol): Loop over languages.  Change
	type of "match_callback".
	(check_match, check_find_bounds_finds)
	(dw2_expand_symtabs_matching): Update.
	(dw2_debug_names_iterator): Add new constructor.
	(dw2_debug_names_map_matching_symbols): New function.
	(dw2_debug_names_expand_symtabs_matching): Update.
	(dwarf2_debug_names_functions): Use
	dw2_debug_names_map_matching_symbols.