community/sdl2: cannot use find_package(SDL2) with CMake

When building xormod with the command cmake -B build, I get this error:

FATAL_ERROR,SDL2::SDL2 doesn't seem to contain any kind of lib to link against in IMPORTED_IMPLIB* or IMPORTED_LOCATION*
CMake Error at /usr/lib/cmake/SDL2/SDL2Config.cmake:94 (get_filename_component):
  get_filename_component called with incorrect number of arguments
Call Stack (most recent call first):
  CMakeLists.txt:5 (find_package)

This seems to have been reported in #12969 (closed), but that was fixed by using sdl-dev since the CMakeLists.txt file for openttd supports building with sdl.