lto: Stream current working directory for first streamed relative filename and adjust...

lto: Stream current working directory for first streamed relative filename and adjust relative paths [PR93865]

If the gcc -c -flto ... commands to compile some or all objects are run in a
different directory (or in different directories) from the directory in
which the gcc -flto link line is invoked, then the .debug_line will be
incorrect if there are any relative filenames, it will use those relative
filenames while .debug_info will contain a different DW_AT_comp_dir.

The following patch streams (at most once after each clear_line_info)
the current working directory (what we record in DW_AT_comp_dir) when
encountering the first relative pathname, and when reading the location info
reads it back and if the current working directory at that point is
different from the saved one, adjusts relative paths by adding a relative
prefix how to go from the current working directory to the previously saved
path (with a fallback e.g. for DOS e:\\foo vs. d:\\bar change to use
absolute directory).

2020-09-10  Jakub Jelinek  <jakub@redhat.com>

	PR debug/93865
	* lto-streamer.h (struct output_block): Add emit_pwd member.
	* lto-streamer-out.c: Include toplev.h.
	(clear_line_info): Set emit_pwd.
	(lto_output_location_1): Encode the ob->current_file != xloc.file
	bit directly into the location number.  If changing file, emit
	additionally a bit whether pwd is emitted and emit it before the
	first relative pathname since clear_line_info.
	(output_function, output_constructor): Don't call clear_line_info
	here.
	* lto-streamer-in.c (struct string_pair_map): New type.
	(struct string_pair_map_hasher): New type.
	(string_pair_map_hasher::hash): New method.
	(string_pair_map_hasher::equal): New method.
	(path_name_pair_hash_table, string_pair_map_allocator): New variables.
	(relative_path_prefix, canon_relative_path_prefix,
	canon_relative_file_name): New functions.
	(canon_file_name): Add relative_prefix argument, if non-NULL
	and string is a relative path, return canon_relative_file_name.
	(lto_location_cache::input_location_and_block): Decode file change
	bit from the location number.  If changing file, unpack bit whether
	pwd is streamed and stream in pwd.  Adjust canon_file_name caller.
	(lto_free_file_name_hash): Delete path_name_pair_hash_table
	and string_pair_map_allocator.