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}