PR sanitizer/77631
	Support for external debug info.
	* elf.c: Include <errno.h>, <sys/stat.h>, <unistd.h>.
	(S_ISLNK): Define if not defined.
	(xstrnlen): Define if strnlen is not available.
	(b_elf_note): Define type.
	(NT_GNU_BUILD_ID): Define macro.
	(elf_crc32, elf_crc32_file): New static functions.
	(elf_is_symlink, elf_readlink): New static functions.
	(elf_open_debugfile_by_buildid): New static function.
	(elf_try_debugfile): New static function.
	(elf_find_debugfile_by_debuglink): New static function.
	(elf_open_debugfile_by_debuglink): New static function.
	(elf_add): Add filename and debuginfo parameters.  Adjust all
	callers.  Look for external debug info notes, and try to fetch
	debug info from external file.
	(struct phdr_data): Add exe_filename field.
	(phdr_callback): Pass filename to elf_add.
	(backtrace_initialize): Add filename parameter.
	* internal.h (backtrace_initialize): Add filename parameter.
	* fileline.c (fileline_initialize): Pass filename to
	backtrace_initialize.
	* pecoff.c (fileline_initialize): Add unused filename parameter.
	* unknown.c (fileline_initialize): Likewise.
	* xcoff.c (fileline_initialize): Likewise.
	* configure.ac: Check for objcopy --add-gnu-debuglink.
	* Makefile.am (dtest): New test target.
	* configure, Makefile.in: Rebuild.

Co-Authored-By: Denis Khalikov <d.khalikov@partner.samsung.com>

From-SVN: r253032