pg_dumpall: Fix handling of conflicting options.

pg_dumpall: Fix handling of conflicting options.

pg_dumpall is missing checks for some conflicting options,
including those passed through to pg_dump.  To fix, introduce a
new function that checks whether mutually exclusive options are
set, and use that in pg_dumpall.  A similar change could likely be
made for pg_dump and pg_restore, but that is left as a future
exercise.

This is arguably a bug fix, but since this might break existing
scripts, no back-patch for now.

Author: Jian He <jian.universality@gmail.com>
Co-authored-by: Nathan Bossart <nathandbossart@gmail.com>
Reviewed-by: Wang Peng <215722532@qq.com>
Reviewed-by: Zsolt Parragi <zsolt.parragi@percona.com>
Reviewed-by: Chao Li <li.evan.chao@gmail.com>
Discussion: https://postgr.es/m/CACJufxFf5%3DwSv2MsuO8iZOvpLZQ1-meAMwhw7JX5gNvWo5PDug%40mail.gmail.com