Fix slowness in gcov (PR gcov-profile/88225).

Fix slowness in gcov (PR gcov-profile/88225).

2018-12-27  Martin Liska  <mliska@suse.cz>

	PR gcov-profile/88225
	* gcov.c(source_info::get_functions_at_location):
	Use newly added line_to_function_map.
	(source_info::add_function): New.
	(output_json_intermediate_file): Use a pointer return
	type for get_functions_at_location.
	(process_all_functions): Use add_function instead
	of direct push to a s->functions container.
	(release_structures): Release ident_to_fn.
	(read_graph_file): Register function into ident_to_fn.
	(read_count_file): Use the map.
	(output_lines): Handle pointer return type of
	get_functions_at_location.

From-SVN: r267431