* 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.