[PATCH] allow empty string as argument to -Map

[Nick Clifton]

Hi Rasmus,

> So, as the next best thing, use a previously bogus value (the empty
> string) as a sentinel to indicate "use the output filename + .map".

Thanks for suggesting this patch.  I have applied it along with a couple
of changes:

  * If a filename is supplied, but it references a directory, then
    create a file inside that directory, again based upon the output
    filename with .map appended.  (I actually did this to make it
    easier to test the new feature, but it strikes that it might be
    useful in its own right).

  * Added a test case.

  * Added an entry to the ld/NEWS file.

  * Updated the --help output from the linker to show that the
    filename is optional.

  * Minor formatting fixes, and the addition of a few comments.

  * Created a ChangeLog entry.

Cheers
  Nick

ld/ChangeLog
2020-05-27  Rasmus Villemoes <rv@rasmusvillemoes.dk>
	    Nick Clifton  <nickc@redhat.com>

	* 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.