Implement more printf length specifiers.

test/printf-test.cc

@@ -350,8 +350,8 @@ TEST(PrintfTest, Length) {
   TestLength<unsigned char>("hh");
   TestLength<short>("h");
   TestLength<unsigned short>("h");
-  //TestLength<long>("l");
-  //TestLength<unsigned long>("l");
+  TestLength<long>("l");
+  TestLength<unsigned long>("l");
   // TODO: more tests
 }