Runtime check for Xkb support in X server.
Contributed patch from Brian Griffin.
Merge 8.5.  Bring together the compile time and run time Xkb checks.
3607830 Runtime checks that Xkb is available in the X server before trying to
use.  Adapted from patch from Brian Griffin.
3607830 Runtime checks that Xkb is available in the X server before trying to
use.  Adapted from patch from Brian Griffin.