c++: constexpr, trivial, and non-alias target [PR111075]

c++: constexpr, trivial, and non-alias target [PR111075]

On Darwin and other targets with !can_alias_cdtor, we instead go to
maybe_thunk_ctor, which builds a thunk function that calls the general
constructor.  And then cp_fold tries to constant-evaluate that call, and we
ICE because we don't expect to ever be asked to constant-evaluate a call to
a trivial function.

No new test because this fixes g++.dg/torture/tail-padding1.C on affected
targets.

	PR c++/111075

gcc/cp/ChangeLog:

	* constexpr.cc (cxx_eval_call_expression): Allow trivial
	call from a thunk.