openmp: Fix ICE on #pragma omp parallel master in template [PR94477]

The following testcase ICEs, because for parallel combined with some
other construct we initialize the omp_parallel_combined_clauses pointer
and expect the construct combined with it to clear it after it no longer
needs it, but OMP_MASTER didn't do that.

2020-04-04  Jakub Jelinek  <jakub@redhat.com>

	PR c++/94477
	* pt.c (tsubst_expr) <case OMP_MASTER>: Clear
	omp_parallel_combined_clauses.

	* g++.dg/gomp/pr94477.C: New test.

gcc/cp/ChangeLog

+2020-04-04  Jakub Jelinek  <jakub@redhat.com>
+
+	PR c++/94477
+	* pt.c (tsubst_expr) <case OMP_MASTER>: Clear
+	omp_parallel_combined_clauses.
+
 2020-04-03  Jason Merrill  <jason@redhat.com>
 
 	PR c++/91966

gcc/cp/pt.c

@@ -18467,8 +18467,10 @@ tsubst_expr (tree t, tree args, tsubst_flags_t complain, tree in_decl,
       add_stmt (t);
       break;
 
-    case OMP_SECTION:
     case OMP_MASTER:
+      omp_parallel_combined_clauses = NULL;
+      /* FALLTHRU */
+    case OMP_SECTION:
       stmt = push_stmt_list ();
       RECUR (OMP_BODY (t));
       stmt = pop_stmt_list (stmt);

gcc/testsuite/ChangeLog

+2020-04-04  Jakub Jelinek  <jakub@redhat.com>
+
+	PR c++/94477
+	* g++.dg/gomp/pr94477.C: New test.
+
 2020-04-03  H.J. Lu  <hongjiu.lu@intel.com>
 
 	PR target/94467

gcc/testsuite/g++.dg/gomp/pr94477.C

+// PR c++/94477
+// { dg-do compile }
+
+void foo ();
+
+template <int>
+void
+bar ()
+{
+  #pragma omp parallel master
+  foo ();
+}
+
+void
+baz ()
+{
+  bar<0> ();
+}