mesa: Implement ARB_clip_control.

mesa: Implement ARB_clip_control.

Implement the mesa parts of ARB_clip_control.
So far no driver enables this.

v3:
Restrict getting clip control state to the availability
of ARB_clip_control.
Move to transformation state.
Handle clip control state with the GL_TRANSFORM_BIT.
Move _FrontBit update into state.c.

Reviewed-by: Brian Paul <brianp@vmware.com>
Signed-off-by: Mathias Froehlich <Mathias.Froehlich@web.de>