As a precursor to the fence sync object video driver
and extension API, move some code from Xext to
miext/sync.  Most of this is just code to set up the
build system to include the new directory.  No
functional code is added in this change.

Signed-off-by: James Jones <jajones@nvidia.com>
Reviewed-by: Keith Packard <keithp@keithp.com>