Extend ld's -Map=<dir> functionality by allowing '%' to be replaced with the output...

Extend ld's -Map=<dir> functionality by allowing '%' to be replaced with the output file path.

	* lexsup.c (parse_args): Add more checks of the mapfile.  If it is
	a directory use the basename of the output file as the file
	component.  If the % character is present, replace it with the
	full output filepath.
	* testsuite/ld-scripts/map-address.exp: Add test of %
	functionality.
	* ld.texi: Document the new behaviour.