openmp: Handle OMP_MASKED in potential_constant_expression_1 [PR103349]

WHen adding OMP_MASKED, I apparently forgot to handle it in
potential_constant_expression_1, which means we can ICE on it.

2021-11-22  Jakub Jelinek  <jakub@redhat.com>

	PR c++/103349
	* constexpr.c (potential_constant_expression_1): Punt on OMP_MASKED.

	* g++.dg/gomp/masked-1.C: New test.

gcc/cp/constexpr.c

@@ -8686,6 +8686,7 @@ potential_constant_expression_1 (tree t, bool want_rval, bool strict, bool now,
     case OMP_SINGLE:
     case OMP_SECTION:
     case OMP_MASTER:
+    case OMP_MASKED:
     case OMP_TASKGROUP:
     case OMP_TARGET_UPDATE:
     case OMP_TARGET_ENTER_DATA:

gcc/testsuite/g++.dg/gomp/masked-1.C

@@ -0,0 +1,14 @@
+// PR c++/103349
+// { dg-do compile { target c++11 } }
+
+int v;
+
+void
+foo (int x, int y)
+{
+  [=] ()
+  {
+#pragma omp masked
+    v = x + y;
+  } ();
+}