glx: Implement GLX_EXT_no_config_context (v2)

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>
6 files changed