Add nacl-clang testing to SCons

tests/threads/race_test.c

 /*
  * Copyright (c) 2012 The Native Client Authors. All rights reserved.
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include <assert.h>
 #include <pthread.h>
 #include <semaphore.h>
 #include <stdio.h>
@@ skipping 34 matching lines @@
     pthread_join(t[i], NULL);
   }
 }
 
 /* Don't let various optimizations (e.g. tail call elimination) to happen. */
 NOINLINE void break_optimization(void) {
 #if defined(__pnacl__)
   volatile int foo;
   foo = 0;
 #else
-  asm volatile ("");
+  __asm__ volatile ("");
 #endif
 }
 
 /* -------------------------------------------------------------------------- */
 /* positive_race_on_global_test
    Simle race on a global variable between three threads.
    We have few stack frames here to test ThreadSanitizer's output. */
 int simple_race_obj;
 NOINLINE void simple_race_write_frame_2(void) {
   break_optimization();
@@ skipping 167 matching lines @@
 /* -------------------------------------------------------------------------- */
 int main(void) {
   if (1) positive_race_on_global_test();
   if (1) positive_race_on_heap_test();
   if (1) positive_wrong_lock_test();
   if (1) negative_locked_access_test();
   if (1) negative_posix_sem_test();
   if (1) thread_create_and_join_test();
   return 0;
 }