frontend: don't ice with pragma NOVECTOR if loop has no condition [PR113267]

In C you can have loops without a condition, the original version of the patch
was rejecting the use of #pragma GCC novector, however during review it was
changed to not due this with the reason that we didn't want to give a compile
error with such cases.

However because annotations seem to be only be allowed on conditions (unless
I'm mistaken?) the attached example ICEs because there's no condition.

This will have it ignore the pragma instead of ICEing.  I don't know if this is
the best solution,  but as far as I can tell we can't attach the annotation to
anything else.

gcc/c/ChangeLog:

	PR c/113267
	* c-parser.cc (c_parser_for_statement): Skip the pragma is no cond.

gcc/testsuite/ChangeLog:

	PR c/113267
	* gcc.dg/pr113267.c: New test.

gcc/c/c-parser.cc

@@ -8445,7 +8445,7 @@ c_parser_for_statement (c_parser *parser, bool ivdep, unsigned short unroll,
  			   build_int_cst (integer_type_node,
 					  annot_expr_unroll_kind),
 			   build_int_cst (integer_type_node, unroll));
-	  if (novector && cond != error_mark_node)
+	  if (novector && cond && cond != error_mark_node)
 	    cond = build3 (ANNOTATE_EXPR, TREE_TYPE (cond), cond,
 			   build_int_cst (integer_type_node,
 					  annot_expr_no_vector_kind),

gcc/testsuite/gcc.dg/pr113267.c

@@ -0,0 +1,8 @@
+/* { dg-do compile } */
+
+void f (char *a, int i)
+{
+#pragma GCC novector
+  for (;;i++)
+    a[i] *= 2;
+}