tcmalloc: Use futex syscall in SpinLockDelay() for ARM.

third_party/tcmalloc/chromium/src/base/spinlock_linux-inl.h

 /* Copyright (c) 2009, Google Inc.
  * All rights reserved.
  * 
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  * 
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 43 matching lines @@
 
 static bool have_futex;
 static int futex_private_flag = FUTEX_PRIVATE_FLAG;
 
 namespace {
 static struct InitModule {
   InitModule() {
     int x = 0;
     // futexes are ints, so we can use them only when
     // that's the same size as the lockword_ in SpinLock.
-#ifdef __arm__
-    // ARM linux doesn't support sys_futex1(void*, int, int, struct timespec*);
-    have_futex = 0;
-#else
     have_futex = (sizeof (Atomic32) == sizeof (int) && 
                   syscall(__NR_futex, &x, FUTEX_WAKE, 1, 0) >= 0);
-#endif
     if (have_futex &&
         syscall(__NR_futex, &x, FUTEX_WAKE | futex_private_flag, 1, 0) < 0) {
       futex_private_flag = 0;
     }
   }
 } init_module;
 
 }  // anonymous namespace
 
 
@@ skipping 24 matching lines @@
 
 void SpinLockWake(volatile Atomic32 *w, bool all) {
   if (have_futex) {
     syscall(__NR_futex, reinterpret_cast<int *>(const_cast<Atomic32 *>(w)),
               FUTEX_WAKE | futex_private_flag, 1, 0);
   }
 }
 
 } // namespace internal
 } // namespace base