PR testsuite/69181: ensure expected multiline outputs is cleared per-test

PR testsuite/69181: ensure expected multiline outputs is cleared per-test

gcc/testsuite/ChangeLog:
	PR testsuite/69181
	* gcc.dg/pr69181-1.c: New test file.
	* gcc.dg/pr69181-2.c: New test file.
	* lib/gcc-dg.exp (dg-test): Consolidate post-test cleanup of
	globals by moving it to...
	(cleanup-after-saved-dg-test): ...this new function.  Add
	"global additional_sources_used".  Add reset of global
	multiline_expected_outputs to the empty list.
	* lib/multiline.exp (_multiline_expected_outputs): Rename this
	global to...
	(multiline_expected_outputs): ...this, and updated comments to
	note that it is modified from gcc-dg.exp.
	(dg-end-multiline-output): Update for the above renaming.
	(handle-multiline-outputs): Likewise.  Remove the clearing
	of the expected outputs to the empty list.

From-SVN: r232535