arch-nspawn should use the correct pacman config file

If arch-nspawn is called with -C, pacman inside the chroot will use
the provided configuration file. This should also be the case for
$pacconf_cmd and pacman outside the chroot.

If arch-nspawn is called without -C, pacman inside the chroot will
use $workdir/etc/pacman.conf -- again, $pacconf_cmd and pacman
outside the chroot should use that, too. So lets just set $pac_conf
in that case.

For example, Arch Linux 32 provides separate pacman configurations
inside /usr/share/devtools which use /etc/pacman.d/mirrorlist32 as
mirrorlist for their build commands (extra-i686-build, etc.). This
way, we can build i686 and x86_64 packages on the same x86_64 host
with very minimal changes to devtools.

arch-nspawn.in

@@ -64,7 +64,7 @@ if (( ${#cache_dirs[@]} == 0 )); then
 fi
 
 # shellcheck disable=2016
-host_mirrors=($($pacconf_cmd --repo extra Server 2> /dev/null | sed -r 's#(.*/)extra/os/.*#\1$repo/os/$arch#'))
+host_mirrors=($($pacconf_cmd --config "${pac_conf:-$working_dir/etc/pacman.conf}" --repo extra Server 2> /dev/null | sed -r 's#(.*/)extra/os/.*#\1$repo/os/$arch#'))
 
 for host_mirror in "${host_mirrors[@]}"; do
 	if [[ $host_mirror == *file://* ]]; then

archbuild.in

@@ -52,7 +52,6 @@ check_root SOURCE_DATE_EPOCH,SRCDEST,SRCPKGDEST,PKGDEST,LOGDEST,MAKEFLAGS,PACKAG
 
 # Pass all arguments after -- right to makepkg
 makechrootpkg_args+=("${@:$OPTIND}")
-cachedir=$(pacman-conf -c "${pacman_config}" CacheDir)
 
 if ${clean_first} || [[ ! -d "${chroots}/${repo}-${arch}" ]]; then
 	msg "Creating chroot for [%s] (%s)..." "${repo}" "${arch}"
@@ -73,7 +72,6 @@ if ${clean_first} || [[ ! -d "${chroots}/${repo}-${arch}" ]]; then
 	setarch "${arch}" mkarchroot \
 		-C "${pacman_config}" \
 		-M "${makepkg_config}" \
-		-c "${cachedir}" \
 		"${chroots}/${repo}-${arch}/root" \
 		"${base_packages[@]}" || abort
 else