discount: use deterministic mangling

`discount` offers a randomized string mangling function which results in
non-deterministic output.

This commit disables the randomized mangling in favor of a deterministic
approach. `discount` has builtin support for this through the
`--debian-glitch` configuration flag.

pkgs/tools/text/discount/default.nix

@@ -26,6 +26,8 @@ stdenv.mkDerivation rec {
     "--pkg-config"
     "--shared"
     "--with-fenced-code"
+    # Use deterministic mangling
+    "--debian-glitch"
   ];
 
   enableParallelBuilding = true;