c++: destroying delete, throw in new-expr [PR100588]

c++: destroying delete, throw in new-expr [PR100588]

The standard says that a destroying operator delete is preferred, but that
only applies to the delete-expression, not the cleanup if a new-expression
initialization throws.  As a result of this patch, several of the destroying
delete tests don't get EH cleanups, but I'm turning off the warning in cases
where the initialization can't throw anyway.

It's unclear what should happen if the class does not declare a non-deleting
operator delete; a proposal in CWG was to call the global delete, which
makes sense to me if the class doesn't declare its own operator new.  If it
does, we warn and don't call any deallocation function if initialization
throws.

	PR c++/100588

gcc/cp/ChangeLog:

	* call.c (build_op_delete_call): Ignore destroying delete
	if alloc_fn.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp2a/destroying-delete5.C: Expect warning.
	* g++.dg/cpp2a/destroying-delete6.C: New test.