[mkchrootpkg] Upstream fixes

- makepkg 5.1 implements error codes, and 14 means that installing the
  packages after they were built has failed. We don't care about this
  error and would like makechrootpkg to succeed regardless, e.g. for split
  packages that are mutually exclusive.
- Do not assume the makechrootpkg user's groupname is the same as the username

bin/mkchrootpkg.in

@@ -242,6 +242,12 @@ _chrootbuild() {
 #     cd /startdir
 #     sudo -u builduser makepkg "$@"
     sudo -iu builduser bash -c 'cd /startdir; makepkg "$@"' -bash "$@"
+
+    ret=$?
+    case $ret in
+        0|14) return 0;;
+        *) return $ret;;
+    esac
 }
 
 _chrootnamcap() {
@@ -254,7 +260,7 @@ _chrootnamcap() {
 
 download_sources() {
     local builddir="$(mktemp -d)"
-    chown $SUDO_USER:$SUDO_USER "$builddir"
+    chown $SUDO_USER: "$builddir"
 
     # Ensure sources are downloaded
     if [[ -n $SUDO_USER ]]; then