AIX:Proposal to use kSemaphoreAlignmentMask instead kPointerAlignmentMask

native_handle_ on AIX64 is of type int, and therefore fails
on an operation with a pointer type. Use
kSemaphoreAlignmentMask as sizeof(int) on AIX and
sizeof(pointer) otherwise.

R=jochen@chromium.org, mbrandy@us.ibm.com

BUG=v8:4767
LOG=N

Review-Url: https://codereview.chromium.org/1936003002
Cr-Commit-Position: refs/heads/master@{#35988}

src/base/platform/semaphore.cc

@@ -78,9 +78,15 @@ Semaphore::Semaphore(int count) {
   // Unaligned native handle can later cause a failure in semaphore signal.
   // Check the alignment here to catch the failure earlier.
   // Context: crbug.com/605349.
-  const uintptr_t kPointerAlignmentMask = sizeof(void*) - 1;
+#if V8_OS_AIX
+  // On aix sem_t is of type int
+  const uintptr_t kSemaphoreAlignmentMask = sizeof(int) - 1;
+#else
+  const uintptr_t kSemaphoreAlignmentMask = sizeof(void*) - 1;
+#endif
   CHECK_EQ(
-      0, reinterpret_cast<uintptr_t>(&native_handle_) & kPointerAlignmentMask);
+      0, reinterpret_cast<uintptr_t>(&native_handle_) &
+      kSemaphoreAlignmentMask);
   DCHECK(count >= 0);
 #if V8_LIBC_GLIBC
   // sem_init in glibc prior to 2.1 does not zero out semaphores.