[PATCH] allow empty string as argument to -Map

 [PATCH] allow empty string as argument to -Map

	* lexsup.c (parse_args): If the map filename is defined but empty
	create a name based upon the output file name.  If the name is
	defined but refers to a directory create a file inside the
	directory based on the output file name.
	* ld.texi: Document the new feature.
	* testsuite/ld-script/map-address.exp: Add test of new feature.
	* NEWS: Mention the new feature.