Add compile-fail test for cfg_target_thread_local

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

Refs: #39059

src/test/compile-fail/auxiliary/cfg-target-thread-local.rs

@@ -0,0 +1,17 @@
+// Copyright 2016 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.
+
+#![feature(thread_local)]
+#![feature(cfg_target_thread_local)]
+#![crate_type = "lib"]
+
+#[no_mangle]
+#[cfg_attr(target_thread_local, thread_local)]
+pub static FOO: u32 = 3;

src/test/compile-fail/feature-gate-cfg-target-thread-local.rs

@@ -0,0 +1,27 @@
+// Copyright 2016 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.
+
+// ignore-windows
+// aux-build:cfg-target-thread-local.rs
+
+#![feature(thread_local)]
+
+extern crate cfg_target_thread_local;
+
+extern {
+    #[cfg_attr(target_thread_local, thread_local)]
+    //~^ `cfg(target_thread_local)` is experimental and subject to change (see issue #29594)
+
+    static FOO: u32;
+}
+
+fn main() {
+    assert_eq!(FOO, 3);
+}

src/tools/tidy/src/features.rs

@@ -167,7 +167,6 @@ pub fn check(path: &Path, bad: &mut bool) {
 
     // FIXME get this whitelist empty.
     let whitelist = vec![
-        "cfg_target_thread_local",
     ];
 
     // Only check the number of lang features.