c++ frontend: check for missing condition for novector [PR115623]

It looks like I forgot to check in the C++ frontend if a condition exist for the
loop being adorned with novector.  This causes a segfault because cond isn't
expected to be null.

This fixes it by issuing ignoring the pragma when there's no loop condition
the same way we do in the C frontend.

gcc/cp/ChangeLog:

	PR c++/115623
	* semantics.cc (finish_for_cond): Add check for C++ cond.

gcc/testsuite/ChangeLog:

	PR c++/115623
	* g++.dg/vect/vect-novector-pragma_2.cc: New test.

(cherry picked from commit 84acbfbecbdbc3fb2a395bd97e338b2b26fad374)

gcc/cp/semantics.cc

@@ -1501,7 +1501,7 @@ finish_for_cond (tree cond, tree for_stmt, bool ivdep, tree unroll,
 				  build_int_cst (integer_type_node,
 						 annot_expr_unroll_kind),
 				  unroll);
-  if (novector && cond != error_mark_node)
+  if (novector && cond && cond != error_mark_node)
     FOR_COND (for_stmt) = build3 (ANNOTATE_EXPR,
 				  TREE_TYPE (FOR_COND (for_stmt)),
 				  FOR_COND (for_stmt),

gcc/testsuite/g++.dg/vect/vect-novector-pragma_2.cc

@@ -0,0 +1,10 @@
+/* { dg-do compile } */
+
+void f (char *a, int i)
+{
+#pragma GCC novector
+  for (;;i++)
+    a[i] *= 2;
+}
+
+