Add test to check for debug logging disabled at compile time

src/test/run-pass/logging-enabled-debug.rs

@@ -0,0 +1,21 @@
+// Copyright 2013 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// xfail-fast
+// compile-flags:--cfg ndebug
+// exec-env:RUST_LOG=logging-enabled-debug=debug
+
+use std::logging;
+
+fn main() {
+    if log_enabled!(logging::DEBUG) {
+        fail!("what?! debugging?");
+    }
+}