For programs linked against the macOS 10.14 SDK, Mojave makes all view
hierarchies layer-backed.  For views to which OpenGL contexts have been
attached this caused a regression where they sometimes failed to render and
just remain black.  Updating the OpenGL context after the framework has
assigned a layer to our view works around the problem.  Thanks to Elviss
Strazdins on Stack Overflow for the solution
<https://stackoverflow.com/a/52938517/1312143>.
Signed-off-by: Ken Thomases <ken@codeweavers.com>
Signed-off-by: Alexandre Julliard <julliard@winehq.org>