ngIRCd: Set "sysconfdir" to #{HOMEBREW_PREFIX}/etc/ngircd

This prevents Homebrew from linking the configuration files into
the "sysconfdir" which would break updates when the user modified
the configuration file(s) ...

Signed-off-by: Alexander Barton <alex@barton.de>
ngircd: update 21.1 bottle.

Closes #27869.

Signed-off-by: Mike McQuaid <mike@mikemcquaid.com>