Add _cocoalayer.mm to CMakeLists

src/CMakeLists.txt

@@ -37,6 +37,7 @@ set(raylib_sources
     rtext.c
     rtextures.c
     utils.c
+    _cocoalayer.mm
     )
 
 # <root>/cmake/GlfwImport.cmake handles the details around the inclusion of glfw