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.

gcc/cp/constexpr.cc

diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc
index dc59f59..4346b29 100644
--- a/gcc/cp/constexpr.cc
+++ b/gcc/cp/constexpr.cc
@@ -3103,6 +3103,9 @@
      we can only get a trivial function here with -fno-elide-constructors.  */
   gcc_checking_assert (!trivial_fn_p (fun)
 		       || !flag_elide_constructors
+		       /* Or it's a call from maybe_thunk_body (111075).  */
+		       || (TREE_CODE (t) == CALL_EXPR ? CALL_FROM_THUNK_P (t)
+			   : AGGR_INIT_FROM_THUNK_P (t))
 		       /* We don't elide constructors when processing
 			  a noexcept-expression.  */
 		       || cp_noexcept_operand);