FindSDL: add support to SDL2
CMake 3.27 & CMake 3.29 cannot automatically find the SDL2 libraries, but if the SDL_INCLUDE_DIR
and SDL_LIBRARY
are filled, all works nice for now.
Values to fill:
set(SDL_INCLUDE_DIR "$ENV{SDLDIR}/include/SDL2")
set(SDL_LIBRARY "$ENV{SDLDIR}/lib/libSDL2.a")