radv: Use build ID if available for cache UUID.

To get an useful UUID for systems that have a non-useful mtime
for the binaries.

I started using SHA1 to ensure we get reasonable mixing in the
various possibilities and the various build id lengths.

CC: <mesa-stable@lists.freedesktop.org>
Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>
(cherry picked from commit d17443a4)