* lib/gcc-dg.exp (dg-process-target): Wrapper for dg function to
	handle effective-target-keyword.
	(dg-skip-if): Support effective-target keyword as target list.
	(dg-xfail-if): Ditto.
	* lib/target-supports.exp (is-effective-target-keyword): New proc.

From-SVN: r91592