Fixed MacOS build after the recent Linux fix caused an issue on
MacOS. Removed a few flags and changed visibility to fix it.

Change-Id: Ic9d08d8ec0ccf8a2002f2787c3ec79861bb59139
Reviewed-on: https://swiftshader-review.googlesource.com/8589Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>