Ignore test case on Windows.

Windows is not #[cfg(target_thread_local)] and as such should link
to the external symbol. But it fails with:

    thread '<main>' panicked at 'assertion failed: `(left == right)` (left: `272246271`, right: `3`)', C:/bot/slave/auto-win-msvc-64-opt/build/src/test/run-pass/thread-local-extern-static.rs:24

src/test/run-pass/thread-local-extern-static.rs

@@ -8,6 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+// ignore-windows
 // aux-build:thread-local-extern-static.rs
 
 #![feature(thread_local)]