C++11 thread_local destructors support

This feature is specifically for the C++ compiler to offload calling
thread_local object destructors on thread program exit, to glibc.
This is to overcome the possible complication of destructors of
thread_local objects getting called after the DSO in which they're
defined is unloaded by the dynamic linker.  The DSO is marked as
'unloadable' if it has a constructed thread_local object and marked as
'unloadable' again when all the constructed thread_local objects
defined in it are destroyed.

nptl/pthread_create.c

@@ -311,6 +311,9 @@ start_thread (void *arg)
 #endif
     }
 
+  /* Call destructors for the thread_local TLS variables.  */
+  __call_tls_dtors ();
+
   /* Run the destructor for the thread-local data.  */
   __nptl_deallocate_tsd ();