xbps-src: prevent builddir/destdir from always being removed

The problem here is that newly introduced behavior in commit
b2b0409be4 resulted in builddir and
destdir *always* being removed when starting a build, as a part of
masterdir auto-update. We don't want this as we may want to resume
a previous build (e.g. by running stages individually or by resuming
a failed build from where it stopped).

Therefore, explicitly override the removal to restore previous behavior.

xbps-src

@@ -712,7 +712,8 @@ case "$XBPS_TARGET" in
             chroot_handler $XBPS_TARGET $XBPS_TARGET_PKG
         else
             chroot_sync_repodata
-            update_base_chroot
+            # prevent update_base_chroot from removing the builddir/destdir
+            update_base_chroot keep-all-force
             $XBPS_LIBEXECDIR/build.sh $XBPS_TARGET_PKG $XBPS_TARGET_PKG \
                 $XBPS_TARGET $XBPS_CROSS_BUILD || exit $?
         fi