How to adapt OpenGL ES 1.1 program to desktop OpenGL?

If I have written a game in C++ that runs on a mobile platform using OpenGL ES 1.1, how do I convert it to run on the desktop which only has OpenGL support?
Is there a simple way to accomplish this or is there always a need for a complex compatibility layer?

What do you use for windowing, sound, input, etc? Because they’re probably going to involve more work if you have to port them - the actual GL code should come over largely unchanged.