Index: libcxxabi/src/cxa_thread_atexit.cpp
===================================================================
--- libcxxabi/src/cxa_thread_atexit.cpp
+++ libcxxabi/src/cxa_thread_atexit.cpp
@@ -27,7 +27,15 @@
   // at runtime, even if libc++ is built against an older libc
   _LIBCXXABI_WEAK
 #endif
+#ifdef __MVS__
+  // FIXME: No __cxa_thread_atexit_impl on z/OS.
+  int __cxa_thread_atexit_impl(Dtor, void*, void*) {
+    abort_message("__cxa_thread_atexit() is not implemented on z/OS");
+    return -1;
+  }
+#else
   int __cxa_thread_atexit_impl(Dtor, void*, void*);
+#endif
 
 #ifndef HAVE___CXA_THREAD_ATEXIT_IMPL
 
@@ -67,9 +75,15 @@
   };
 
   // The linked list of thread-local destructors to run
-  __thread DtorList* dtors = nullptr;
+#ifndef __MVS__
+  __thread
+#endif
+  DtorList* dtors = nullptr;
   // True if the destructors are currently scheduled to run on this thread
-  __thread bool dtors_alive = false;
+#ifndef __MVS__
+  __thread
+#endif
+  bool dtors_alive = false;
   // Used to trigger destructors on thread exit; value is ignored
   std::__libcpp_tls_key dtors_key;