Nuke the last vestiges of printing pid_t values with the wrong
types, at least in code compiled on mingw64.  There may be other
places, but for now they are only compiled on systems where the
existing %d doesn't trigger gcc warnings.

* src/rpc/virnetsocket.c (virNetSocketNew): Use %lld and casting,
rather than assuming any particular int type for pid_t.
* src/util/command.c (virCommandRunAsync, virPidWait)
(virPidAbort): Likewise.
(verify): Drop a now stale assertion.