middle-end/119119 - re-gimplification of empty CTOR assignments

The following testcase runs into a re-gimplification issue during
inlining when processing

  MEM[(struct e *)this_2(D)].a = {};

where re-gimplification does not handle assignments in the same
way than the gimplifier but instead relies on rhs_predicate_for
and gimplifying the RHS standalone.  This fails to handle
special-casing of CTORs.  The is_gimple_mem_rhs_or_call predicate
already handles clobbers but not empty CTORs so we end up in
the fallback code trying to force the CTOR into a separate stmt
using a temporary - but as we have a non-copyable type here that ICEs.

The following generalizes empty CTORs in is_gimple_mem_rhs_or_call
since those need no additional re-gimplification.

	PR middle-end/119119
	* gimplify.cc (is_gimple_mem_rhs_or_call): All empty CTORs
	are OK when not a register type.

	* g++.dg/torture/pr11911.C: New testcase.

gcc/gimplify.cc

@@ -607,7 +607,7 @@ is_gimple_mem_rhs_or_call (tree t)
   else
     return (is_gimple_val (t)
 	    || is_gimple_lvalue (t)
-	    || TREE_CLOBBER_P (t)
+	    || (TREE_CODE (t) == CONSTRUCTOR && CONSTRUCTOR_NELTS (t) == 0)
 	    || TREE_CODE (t) == CALL_EXPR);
 }

gcc/testsuite/g++.dg/torture/pr11911.C

+// { dg-do compile }
+// { dg-require-effective-target c++17 }
+
+struct b {
+  int a;
+};
+struct c {
+  b d{};
+  c() = default;
+  c(c &) = delete;
+};
+struct e {
+  c a{};
+  e() {}
+};
+inline e f() { return {}; }
+struct g {
+  e cx;
+  g() : cx{f()} {}
+};
+void h() { g i; }