[wasm] Move the semaphore for parallel compilation to the wasm module.

src/base/platform/semaphore.cc

 // Copyright 2013 the V8 project 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 "src/base/platform/semaphore.h"
 
 #if V8_OS_MACOSX
 #include <mach/mach_init.h>
 #include <mach/task.h>
 #endif
@@ skipping 83 matching lines @@
 
 
 Semaphore::~Semaphore() {
   int result = sem_destroy(&native_handle_);
   DCHECK_EQ(0, result);
   USE(result);
 }
 
 void Semaphore::Signal() {
   int result = sem_post(&native_handle_);
+  // This check may fail with libc-2.19, which we use on the try bots, if the

[Michael Lippautz, 2016/06/22 10:34:46]

nit: Maybe just write that it fails for <libc-2.21?

+  // semaphore is destroyed while sem_post is still executed. A work around is
+  // to extend the lifetime of the semaphore. The problem got fixed in
+  // libc-2.21.
   CHECK_EQ(0, result);
 }
 
 
 void Semaphore::Wait() {
   while (true) {
     int result = sem_wait(&native_handle_);
     if (result == 0) return;  // Semaphore was signalled.
     // Signal caused spurious wakeup.
     DCHECK_EQ(-1, result);
@@ skipping 91 matching lines @@
       DCHECK(result == WAIT_OBJECT_0);
       return true;
     }
   }
 }
 
 #endif  // V8_OS_MACOSX
 
 }  // namespace base
 }  // namespace v8