Commit 94ab7455 added SA_RESTART to the SIGALRM handler. However, the
Popen code tears down and recreates the SIGALRM handler via OsSignal(),
and this flag is dropped at this time.
Clean the code to use just a single codepath for creating this signal
handler, always applying SA_RESTART.
[ajax: Fixed commit id]
Reviewed-by: Adam Jackson <ajax@redhat.com>
Signed-off-by: Daniel Drake <drake@endlessm.com>