Merge branch SRB2:next into improve-backtrace

.gitlab-ci.yml

CMakeLists.txt

doc/specs/udmf_srb2.txt

extras/conf/udb/Includes/SRB222_misc.cfg

libs/SDL2/WhatsNew.txt

libs/SDL2/docs/README-android.md

libs/SDL2/docs/README-dynapi.md

libs/SDL2/docs/README-emscripten.md

libs/SDL2/docs/README-gdk.md

libs/SDL2/docs/README-ios.md

libs/SDL2/i686-w64-mingw32/bin/SDL2.dll

libs/SDL2/i686-w64-mingw32/bin/sdl2-config

libs/SDL2/i686-w64-mingw32/include/SDL2/SDL.h

libs/SDL2/i686-w64-mingw32/include/SDL2/SDL_assert.h

libs/SDL2/i686-w64-mingw32/include/SDL2/SDL_atomic.h

libs/SDL2/i686-w64-mingw32/include/SDL2/SDL_audio.h

libs/SDL2/i686-w64-mingw32/include/SDL2/SDL_bits.h

libs/SDL2/i686-w64-mingw32/include/SDL2/SDL_blendmode.h

libs/SDL2/i686-w64-mingw32/include/SDL2/SDL_clipboard.h

libs/SDL2/i686-w64-mingw32/include/SDL2/SDL_config.h