Fix -fuse-ld option to accept string argument.

Fix -fuse-ld option to accept string argument.

PR 22042 complained that garbage text was being printed in the help
for the -fuse-ld option; this was caused by passing an empty string
to the gettext() function, which sometimes returns garbage when passed
an empty string. The quick fix was to replace "" with NULL as the helparg,
but that changed the parsing of the option, as gold uses the helparg to
determine whether an option takes an argument. This patch adds a
non-empty helparg string to fix both problems.

gold/
	PR gold/22694
	* options.h (-fuse-ld): Add correct helparg.