The "result" argument to functions get(pwu|grg)id_r and get(pw|gr)name_r
does not appear in the signatures provided on older platforms. We set
the pointer to the result memory in case the function ignores it, thus
ensuring initialization.
The commit "Fixed a few of the SunOS build errors in libarchive" changed
the call to these functions to use the old signatures. Instead we now
define _XOPEN_SOURCE to get the improved modern signatures.
This allows for a built in bzip and zip capability, so external tools
will not be needed for these packagers. The cmake -E tar xf should be
able to handle all compression types now as well.