test for a rather simply gcc optimization

[r22409]

ir/be/test/global_null_test.c

+static void f1(void) {
+	printf("f1\n");
+}
+
+static void f2(void) {
+	printf("f2\n");
+}
+
+int test(char *x)
+{
+  char ret = *x;
+
+  if (x)
+    f1();
+  else
+    f2();
+  return ret;
+}
+
+int main(int argc, char *argv[]) {
+	char x = '\0';
+
+	return test(&x);
+}