Windows: Use mtafsutil library when linking with pthreads

Use the multi-threaded version of the util library in a few places
that are linking with pthreads but use the standard version.

Change-Id: If4b72d4785fb3bfac9b7c133d323ebf95c72f804
Reviewed-on: http://gerrit.openafs.org/9844
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>