configure.ac forces sysconfdir to be /etc, breaking Nix/Guix installs

[xelxebar]

Overview

Line 144 in configure.ac is a little strange:

test "$sysconfdir" = '${prefix}/etc' && sysconfdir=/etc

It strips the prefix from sysconfdir. I'm not sure what the intent is here, but this breaks installations anywhere other than the root directory. In particular, Guix and Nix will issue a build failure, since the build daemon doesn't have permission to create things under /etc.

Proposal

Perhaps the && was intended to be || or something? Better yet, maybe we want to set sysconfdir via an autoconf macro instead?