NULLREGION means that the entire window should be clipped out, and its
children displayed instead. The change broke some offscreening decisions
when both parent and children have a GL drawable created but drawing
actually happens on the child window.
(Found while trying to reproduce otherwise unrelated regression in
https://bugs.winehq.org/show_bug.cgi?id=52738, the game there uses ddraw
and doesn't display anything after 786d9d1685ac220081b10cc779d4d331ddd2fc52)
Fixes: 786d9d1685ac220081b10cc779d4d331ddd2fc52
Wine-Bug: https://bugs.winehq.org/show_bug.cgi?id=57503
--
v2: winex11: Move GL/VK offscreen if the clipping region is NULLREGION.
winex11: Use DCX_USESTYLE when checking DC clipping regions.
https://gitlab.winehq.org/wine/wine/-/merge_requests/7014
The preprocessor condition to cover pre-2013 VisualStudio around
C99 support actually also admitted current versions of GCC and
breaks GCC in C23 mode.
Address this by explicitly checking for GCC which, by definition,
then does not qualify as VisualStudio.
--
v3: capstone: Avoid GCC being treated as old VisualStudio
https://gitlab.winehq.org/wine/wine/-/merge_requests/7040