Include timers when using cmake (#29)

CMakeLists.txt

@@ -796,6 +796,16 @@ if(EMSCRIPTEN)
     set(SOURCE_FILES ${SOURCE_FILES} ${EM_POWER_SOURCES})
     set(HAVE_SDL_POWER TRUE)
   endif()
+  if(SDL_TIMERS)
+    set(SDL_TIMER_UNIX 1)
+    file(GLOB TIMER_SOURCES ${SDL2_SOURCE_DIR}/src/timer/unix/*.c)
+    set(SOURCE_FILES ${SOURCE_FILES} ${TIMER_SOURCES})
+    set(HAVE_SDL_TIMERS TRUE)
+
+    if(CLOCK_GETTIME)
+      set(HAVE_CLOCK_GETTIME 1)
+    endif()
+  endif()
   if(SDL_VIDEO)
     set(SDL_VIDEO_DRIVER_EMSCRIPTEN 1)
     file(GLOB EM_VIDEO_SOURCES ${SDL2_SOURCE_DIR}/src/video/emscripten/*.c)