Fix PRs 106764, 106765, and 107307, all ICE after invalid re-declaration

The problem here is the gimplifier returns GS_ERROR but
in some cases we don't check that soon enough and try
to do other work which could crash.
So the fix in these two cases is to return GS_ERROR
early if the gimplify_* functions had return GS_ERROR.

OK? Bootstrapped and tested on x86_64-linux-gnu with no regressions.

Thanks,
Andrew Pinski

gcc/ChangeLog:

	PR c/106764
	PR c/106765
	PR c/107307
	* gimplify.cc (gimplify_compound_lval): Return GS_ERROR
	if gimplify_expr had return GS_ERROR.
	(gimplify_call_expr): Likewise.

gcc/testsuite/ChangeLog:

	PR c/106764
	PR c/106765
	PR c/107307
	* gcc.dg/redecl-19.c: New test.
	* gcc.dg/redecl-20.c: New test.
	* gcc.dg/redecl-21.c: New test.