cmake: enable SDL_TEST by default for emscripten

CMakeLists.txt

@@ -383,7 +383,6 @@ if(EMSCRIPTEN)
   set(SDL_ATOMIC_ENABLED_BY_DEFAULT OFF)
   set(SDL_LOADSO_ENABLED_BY_DEFAULT OFF)
   set(SDL_CPUINFO_ENABLED_BY_DEFAULT OFF)
-  set(SDL_TEST_ENABLED_BY_DEFAULT OFF)
 endif()
 
 if(VITA OR PSP OR PS2 OR N3DS)