terminus_font: reliably generate fontdir

`fonts.dir` and `fonts.scale` are created by `make fontdir` by running
`mkfontscale` and `mkfontdir` for the output directory, which means the
`install` targets must have completed first. This is not known to `make`,
though, so we need to disable paralellism to make sure the jobs are
executed sequentially.

pkgs/data/fonts/terminus-font/default.nix

@@ -24,6 +24,9 @@ stdenv.mkDerivation rec {
   '';
 
   installTargets = [ "install" "install-otb" "fontdir" ];
+  # fontdir depends on the previous two targets, but this is not known
+  # to make, so we need to disable parallelism:
+  enableParallelInstalling = false;
 
   meta = with lib; {
     description = "A clean fixed width font";