For a few test cases, clarify dependance on effective-target 'nonlocal_goto' into 'exceptions'

For example, for nvptx, these test cases currently indeed fail with
'sorry, unimplemented: target cannot support nonlocal goto'.  However,
that's just an artefact of non-existing support for exception handling,
and these test cases already require effective-target 'exceptions'.

	gcc/testsuite/
	* gcc.dg/cleanup-12.c: Don't 'dg-skip-if "" { ! nonlocal_goto }'.
	* gcc.dg/cleanup-13.c: Likewise.
	* gcc.dg/cleanup-5.c: Likewise.
	* gcc.dg/gimplefe-44.c: Don't
	'dg-require-effective-target nonlocal_goto'.