It doesn't appear to work anymore, and was disabled by default anyhow, since
the needed APIs are forbidden on the Mac App Store.
A better solution to lock the mouse to the window on macOS would still be
welcome. CGAssociateMouseAndMouseCursorPosition() works fine for relative
mouse mode, this was just a question of SDL_SetWindowGrab(). As it stands
now, a grabbed mouse can briefly break out of the window, causing varying
degrees of chaos.
The internal function SDL_EGL_LoadLibrary() did not delete and remove a mostly
uninitialized data structure if loading the library first failed. A later try to
use EGL then skipped initialization and assumed it was previously successful
because the data structure now already existed. This led to at least one crash
in the internal function SDL_EGL_ChooseConfig() because a NULL pointer was
dereferenced to make a call to eglBindAPI().
