🔨 CMake: Better error message for bad SDL2 configs

CMakeLists.txt

@@ -203,11 +203,13 @@ else()
   find_package(SDL2 REQUIRED)
   if(TARGET SDL2::SDL2)
     set(SDL2_TARGET SDL2::SDL2)
-  else()
+  elseif(TARGET SDL2::SDL2-static)
     # On some distros, such as vitasdk, only the SDL2::SDL2-static target is available.
     set(SDL2_TARGET SDL2::SDL2-static)
     # Alias to SDL2::SDL2 because some finder scripts may refer to SDL2::SDL2.
     add_library(SDL2::SDL2 ALIAS SDL2::SDL2-static)
+  else()
+    message(FATAL_ERROR "SDL2 cmake config found but it does not define SDL2::SDL2 nor SDL2::SDL2-static")
   endif()
   find_package(SDL2_ttf REQUIRED)
   find_package(SDL2_mixer REQUIRED)