This more or less ports EGL_KHR_no_config_context to GLX.
v2: Enable the extension only for those backends that support it.
Khronos: https://github.com/KhronosGroup/OpenGL-Registry/pull/102 Reviewed-by: Kenneth Graunke <kenneth@whitecape.org> Signed-off-by: Adam Jackson <ajax@redhat.com>