Using GLX on Apple?
I am trying to add glad to an existing project that was written a long time ago to use OpenGL 1.x.  I'd like access to OpenGL 2.1 functions to use shaders.

The project (https://github.com/dmurdoch/rgl) was originally written with three sets of fixed loaders, for Win32, AGL, and GLX.  I dropped the AGL code some years ago, and started using GLX on Apple (provided by XQuartz).

I'd like to use glad now to hopefully simplify things a bit, so I don't have to write a loader for the shader functions completely from scratch.

On a Mac, glad appears to be using native Apple OpenGL, so I'm making changes to the generated loader.  So far I have made these changes:

 - defined GLAD_PLATFORM_APPLE to always be 0, so we're working in GLX.
 - added the Apple lib locations to the list that glad_gl_dlopen_handle looks in.
 
With those changes, I see this:

  - it finds the OpenGL lib
  - it fails to find `glXGetProcAddressARB`
  - it finds `glGetString`
  - when it calls `glad_glGetString(GL_VERSION)`, it receives `NULL`, and quits.

Now I'm stumped.  Have I missed some necessary step?