houdini: make unwrapped installation an optionally fixed derivation

pkgs/by-name/ho/houdini/runtime-build.nix

@@ -1,5 +1,5 @@
-{ stdenv, bc, version, src, eulaDate }:
-stdenv.mkDerivation {
+{ stdenv, bc, version, src, eulaDate, outputHash ? null }:
+stdenv.mkDerivation ({
   inherit version src;
   pname = "houdini-runtime";
 
@@ -16,7 +16,12 @@ stdenv.mkDerivation {
                       --accept-EULA ${eulaDate} \
                       $out
     echo "licensingMode = localValidator" >> $out/houdini/Licensing.opt  # does not seem to do anything any more. not sure, official docs do not say anything about it
+    sed -i 's@'"$out"'@$HFS@g' $out/packages/package_dirs.json  # this seem to be internal houdini tools unavailable to users anyway, but they break fixed-derivation
   '';
 
   dontFixup = true;
-}
+} // (if isNull outputHash then {} else {
+  inherit outputHash;
+  outputHashAlgo = "sha256";
+  outputHashMode = "recursive";
+}))