Suppress cmp component version error messages

Suppress cmp component version error messages

When we use cmp to determine whether to replace
AFS_component_version_number.c, suppress stderr in addition to stdout,
to slightly reduce output during the build.

Reviewed-on: http://gerrit.openafs.org/4471
Reviewed-by: Simon Wilkinson <sxw@inf.ed.ac.uk>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
(cherry picked from commit 21578144e08d46eeec9a2944e92e8d0d7a6dba57)

Change-Id: Ie06f293e3750abb7514ee3795c1af41a26f46642
Reviewed-on: http://gerrit.openafs.org/5770
Reviewed-by: Derrick Brashear <shadow@dementix.org>
Tested-by: Derrick Brashear <shadow@dementix.org>