Fixup for OS X after cd85ff0a814ce38d4704b4b808269d89cdaf0d11

We want to bypass all of this test on OS X and Windows in this branch,
still. So the test added must be inside the #if !defined(MACOSX) &&
!defined(WNT).

Change-Id: I39aa7459bf6a67d445b50be2ad1ca2cdc9022d85