Some platforms, like NonStop do not automatically restart fsync()
when interrupted by a signal, even when that signal is setup with
SA_RESTART.
This can lead to test breakage, e.g., where "--progress" is used,
thus SIGALRM is sent often, and can interrupt an fsync() syscall.
Make sure we deal with such a case by retrying the syscall
ourselves. Luckily, we call fsync() fron a single wrapper,
fsync_or_die(), so the fix is fairly isolated.