mfdg.exp (additional_prunes): New global.

	* testsuite/lib/mfdg.exp (additional_prunes): New global.
	(dg-test): Clear additional_prunes before test is run.
	(dg-prune-output): New procedure.
	* testsuite/lib/libmudflap.exp (libmudflap-dg-test): Do not call
	prune_gcc_output.
	(libmudflap-dg-prune): New procedure.
	* testsuite/libmudflap.c++/pass57-frag.cxx (dg-prune-output):
	New dg directive.

From-SVN: r159440