This is a stricter version of the change made in
{rBbb872b25f219d1a9bc2446228b6dc}
Cmake must never look into Frameworks when the system
library guards (`without_system_libs_begin`/`without_system_libs_end`)
are present.
OpenAL didn't follow this and OpenAL.framework in Xcode would be used.
The Cmake's `FindOpenAL.cmake` looks for both library (in this case,
the .framework file), and include dir.
Precompiled libraries don't contain the former. So `find_package`
cannot be used, or it becomes the hack that {rBb2c707747da9} removed.
So hardcode the include dir path, and other variables.
Reviewed By: brecht
Differential Revision: https://developer.blender.org/D9267
83124856d0