Add missing #ifndef _LIBCPP_NO_EXCEPTIONS around throw in include/thread.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@178237 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/include/thread b/include/thread
index e21a09f..8d3aab2 100644
--- a/include/thread
+++ b/include/thread
@@ -144,9 +144,11 @@
 __thread_specific_ptr<_Tp>::__thread_specific_ptr()
 {
     int __ec = pthread_key_create(&__key_, &__thread_specific_ptr::__at_thread_exit);
+#ifndef _LIBCPP_NO_EXCEPTIONS
     if (__ec)
         throw system_error(error_code(__ec, system_category()),
                            "__thread_specific_ptr construction failed");
+#endif
 }
 
 template <class _Tp>