[PATCH v2 2/4] Output file checksums in CodeView section

[PATCH v2 2/4] Output file checksums in CodeView section

Outputs the file name and MD5 hash of the main source file into the
CodeView .debug$S section, along with that of any #include'd files.

gcc/
	* dwarf2codeview.cc (DEBUG_S_STRINGTABLE): Define.
	(DEBUG_S_FILECHKSMS, CHKSUM_TYPE_MD5, HASH_SIZE): Likewise.
	(codeview_string, codeview_source_file): New structures.
	(struct string_hasher): New class for codeview_string hashing.
	(files, last_file, num_files, string_offset): New variables.
	(strings_hstab, strings, last_string): Likewise.
	(add_string, codevie_start_source_file): New functions.
	(write_strings_tabe, write_soruce_files): Likewise.
	(codeview_debug_finish): Call new functions.
	* dwarf2codeview.h (codeview_start_source_file): Prototype.
	* dwarf2out.cc (dwarf2out_start_source_file): Handle codeview.