More tar portability adjustments.

More tar portability adjustments.

For the three implementations that have caused problems so far:

* GNU and BSD (libarchive) tar both understand --format=ustar
* ustar doesn't support large UID/GID values, so set them to 0 to
  avoid a hard error from at least GNU tar
* OpenBSD tar needs -F ustar, and it appears to warn but carry
  on with "nobody" if a UID is too large
* -f /dev/null is a more portable way to throw away the output, since
  the default destination might be a tape device depending on build
  options that a distribution might change
* Windows ships BSD tar but lacks /dev/null, so ask perl for its name

Based on their manuals, the other two implementations the tests are
likely to encounter in the wild don't seem to need any special handling:

* Solaris/illumos tar uses ustar and replaces large UIDs with 60001
* AIX tar uses ustar (unless --format=pax) and truncates large UIDs

Backpatch-through: 18
Co-authored-by: Thomas Munro <thomas.munro@gmail.com>
Co-authored-by: Sami Imseih <samimseih@gmail.com> (large UIDs)
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us> (earlier version)
Reviewed-by: Nazir Bilal Yavuz <byavuz81@gmail.com> (OpenBSD)
Reviewed-by: Andrew Dunstan <andrew@dunslane.net> (Windows)
Discussion: https://postgr.es/m/3676229.1775170250%40sss.pgh.pa.us
Discussion: https://postgr.es/m/CAA5RZ0tt89MgNi4-0F4onH%2B-TFSsysFjMM-tBc6aXbuQv5xBXw%40mail.gmail.com