libcc1: Fix up libcc1 configure [PR98330]

Either we should write test x$darwin_dynamic_lookup = xyes
or we should make sure the variable is always defined to non-empty string.

2020-12-18  Jakub Jelinek  <jakub@redhat.com>

	PR bootstrap/98380
	* configure.ac: Set darwin_dynamic_lookup=no instead to empty
	string.
	* configure: Regenerated.