[libc++abi] Disable failing test on Darwin

[smeenai]

Summary

The macOS thread-local variable finalizer routines do not handle the
case where a termination function registers another termination function
correctly, causing this test to fail. I've filed a radar for this;
disable the test in the meantime. See [1] for more details.

[1] http://lists.llvm.org/pipermail/cfe-dev/2016-November/051376.html

[EricWF]

If this caused by a bug it should be marked XFAIL and have a comment explaining why it fails and links to the relevant PR's.

Feel free to commit after making those changes.

[ldionne]

Note for posterity in case someone does some archeology and ends up here (as I am doing): the Radar number is 29523281.

libcxxabi/trunk/test/thread_local_destruction_order.pass.cpp

 //===-------------- thread_local_destruction_order.pass.cpp ---------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is dual licensed under the MIT and the University of Illinois Open
 // Source Licenses. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 
+// Darwin TLV finalization routines fail when creating a thread-local variable
+// in the destructor for another thread-local variable:
+// http://lists.llvm.org/pipermail/cfe-dev/2016-November/051376.html
+// XFAIL: darwin
 // UNSUPPORTED: c++98, c++03
 // UNSUPPORTED: libcxxabi-no-threads
 
 #include <cassert>
 #include <thread>
 
 int seq = 0;