make-release: Switch to xz for source releases

make-release

@@ -52,7 +52,7 @@ find . -name autom4te.cache |
  xargs rm -r
 cd ..
 zip -r "$OUTDIR/${sw}.zip" "$sw"
-tar cjvpf "$OUTDIR/${sw}.tbz2" "$sw"
+tar -cJvpf "$OUTDIR/${sw}.txz" "$sw"
 SRCDIR="$TMPDIR/$sw"
 
 dlls='