Fixes building SubzeroTest on Mac.

Change-Id: I8ca1f2ea8101bec496b8e9741c38025ff932b3d6
Reviewed-on: https://swiftshader-review.googlesource.com/17189Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Tested-by: Nicolas Capens <nicolascapens@google.com>