Review of patch that uses "volatile sig_atomic_t"

Hi,

I just put D41265 up on phabricator. It is a trivial
change to mountd.c that defines the variable set
by got_sighup() (the SIGHUP handler) as
   static volatile sig_atomic_t
instead of
    static int

I did list a couple of reviewers, but if you are familiar
with this C requirement, please take a look at it and
review it.

Thanks, rick
ps: I was unaware of this C requirement until Peter Eriksson
      reported it to me yesterday. Several of the other NFS
      related daemons probably need to same fix, which I will
      do after this is reviewed.