Windows: Move grmutex, etc. to afspthread.dll

afsauthent.dll exported:

  pthread_recursive_mutex_lock
  pthread_recursive_mutex_unlock
  grmutex (DATA)

even though a dedicated afspthread.dll existed and all pthreaded
modules must link to afspthread.dll and not all link to
afsauthent.dll.  Move these functions and the global mutex variable
to afspthread.dll to ensure that only one instance of the variable
is present in any binary.

Also remove from src/libafsauthent/NTMakefile the local building
of src/util object files and link to mtafsutil.lib.

Change-Id: I9f8e76165f9c1b1be7ed1a90cdaac03b629d9591
Reviewed-on: http://gerrit.openafs.org/9303
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>