c++: cleanup constant-init'd members [PR96876]

c++: cleanup constant-init'd members [PR96876]

This is a case missed by my recent fixes to aggregate initialization and
exception cleanup for PR94041 et al: we also need to clean up members with
constant initialization if initialization of a later member throws.

It also occurs to me that we needn't bother building the cleanups if
-fno-exceptions; build_vec_init already doesn't.

	PR c++/96876

gcc/cp/ChangeLog:

	* typeck2.cc (split_nonconstant_init_1): Push cleanups for
	preceding members with constant initialization.
	(maybe_push_temp_cleanup): Do nothing if -fno-exceptions.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp1z/aggr-base11.C: New test.
	* g++.dg/eh/aggregate2.C: New test.