Workaround for borked sem_init library function.

This adds a workaround that zeroes out semaphores before they are
initialized. Some versions of sem_init (e.g. GLIBC_2.0) fail to fully
zero out the semaphore, leading to {errno == ENOSYS} with subsequent
sem_timedwait calls.

R=machenbach@chromium.org
BUG=chromium:536813
LOG=n

Review URL: https://codereview.chromium.org/1407463002

Cr-Commit-Position: refs/heads/master@{#31232}

src/base/platform/semaphore.cc

@@ -75,6 +75,10 @@ bool Semaphore::WaitFor(const TimeDelta& rel_time) {
 
 Semaphore::Semaphore(int count) {
   DCHECK(count >= 0);
+#if V8_LIBC_GLIBC
+  // sem_init in glibc prior to 2.1 does not zero out semaphores.
+  memset(&native_handle_, 0, sizeof(native_handle_));
+#endif
   int result = sem_init(&native_handle_, 0, count);
   DCHECK_EQ(0, result);
   USE(result);