test: XFAIL windows for non-portable test

This test validates that the lock_guard is declared variadically across
C++03 and C++11.  Given the lack of stable ABI on Windows and the fact
that the RTTI encoding on Windows is different, XFAIL it on that target.

llvm-svn: 294720

libcxx/test/libcxx/thread/thread.mutex/thread.lock/thread.lock.guard/variadic_mutex_mangling.pass.cpp

@@ -12,6 +12,7 @@
 // TODO(EricWF) Investigate why typeid(...).name() returns a different string
 // on GCC 4.9 but not newer GCCs.
 // XFAIL: gcc-4.9
+// XFAIL: windows
 
 // THIS TESTS C++03 EXTENSIONS.