They're needed on MacOS as SDL_opengl_gletx.h doesn't define them there.
They don't actually work on MacOS, so long-term, the code that uses
these defines should be changed to use #ifdef to check they're available
before using them.
Multiview shaders.
Refactor Frustum management
Rewrite shared shadow map
cull mask should respect stereo
Stereo savegame screencap
LocalMap refactoring
use the vertex buffer hint instead of the display list patch to enable/disable display lists
Character preview fixes