* configure.ac: Check for chsize and posix_fallocate. Replace

	* configure.ac: Check for chsize and posix_fallocate.  Replace
	ftruncate.
	* ftruncate.c: New file, from gnulib.
	* output.cc (posix_fallocate): Define dummy version if not
	HAVE_POSIX_FALLOCATE.
	(Output_file::map): Call posix_fallocate rather than lseek and
	write.
	* gold.h (ftruncate): Declare if not HAVE_FTRUNCATE.
	* configure, Makefile.in, config.in: Rebuild.