Any old UE3 devs know about OpenGL for macOS? Problem with OpenGLResources.h

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I know this is a long shot, but do any of you have experience with UE3? Do you remember building a game to run on OS X or macOS? I’m a total beginner at C++ so I’m not entirely sure about any of this. Right now I’m able to get the game to compile, but when the game starts, it exits with the error
OpenGLDrv/Inc/OpenGLResources.h(238): Assertion failed: Data != NULL

This is the problematic code in OpenGLResources.h:

BYTE *Data = (BYTE *)glMapBuffer(Type, Access);
...
check(Data != NULL); // Data is NULL, so the game exits

I try tracking down glMapBuffer, and I think this is where it should be getting set:
OpenGLWindowsLoader.cpp

#if _WINDOWS // There's literally nothing in this file if I build for Mac.
...
void LoadWindowsOpenGL()
{
	void *GLDll = appGetDllHandle(TEXT("opengl32.dll"));
	// If I try running this on a Mac, it won't do any good because I can't use that dll
	if (!GLDll)
	{
		appErrorf(TEXT("Couldn't load opengl32.dll"));
		return;
	}
	...
	// This is where glMapBuffer should get set.
	glMapBuffer = (PFNGLMAPBUFFERPROC)((void*)wglGetProcAddress("glMapBuffer"));
	...
}
...
#endif

I don’t have a any kind of similar OpenGLMacLoader file and I’m not sure how I can get all of this functionality for Mac. Any advice on what I should do next?