If called from background threads, use Grand Central Dispatch to use the
main thread instead. On the main thread, just call them directly.
Fixes Bugzilla #4932.
This was to deal with broken vsync support in macOS 10.14, which we assumed
would remain broken indefinitely, but a later 10.14 released fixed it.
This is a loss of late-swap support, but there are several subtle problems
in our CVDiplayLink code that are also evaporating, to be fair.
Fixes Bugzilla #4575.
(Backed out changeset 8760fed23001)
Not only does this fix macOS 10.14 ("Mojave")'s broken NSOpenGLCPSwapInterval
support, it also lets us implement "adaptive vsync" on macOS!
CVDisplayLink is supported back to macOS 10.4 ("Tiger"), so we just use it
universally without version checks and dump NSOpenGLCPSwapInterval, Mojave or
not.
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().
