[SDL] OpenGL cross-compile mingw32

[Sam Lantinga]

> This is not a cross compilation error; libopengl should not contain *any*
> references to any extensions. You have to resolve the addresess at runtime.
> Check out any source that uses opengl extensions and you'll find some code
> like this: (windows specific here)
> LockArrays = (PFNGLLOCKARRAYSSGIPROC)wglGetProcAddress("glLockArraysSGI");

> UnlockArrays =
> (PFNGLUNLOCKARRAYSSGIPROC)wglGetProcAddress("glUnlockArraysSGI");

When using SDL, you can use SDL_GL_GetProcAddress("glUnlockArraysSGI");

See ya,
	-Sam Lantinga, Lead Programmer, Loki Entertainment Software