blightmud: use rustPlatform.bindgenHook

By using `rustPlatform.bindgenHook` as a `nativeBuildInput` the
Blightmud derivation's custom LIBCLANG_PATH and preBuild step can be
removed outright. See the languages frameworks Rust hooks docs[0] for
more information.

[0]: https://github.com/NixOS/nixpkgs/blob/master/doc/languages-frameworks/rust.section.md#hooks-hooks

pkgs/games/blightmud/default.nix

@@ -16,33 +16,10 @@ rustPlatform.buildRustPackage rec {
 
   buildFeatures = lib.optional withTTS "tts";
 
-  nativeBuildInputs = [ pkg-config ];
+  nativeBuildInputs = [ pkg-config rustPlatform.bindgenHook ];
 
   buildInputs = [ alsa-lib openssl ] ++ lib.optional withTTS [ speechd ];
 
-  # Building the speech-dispatcher-sys crate for TTS support requires setting
-  # LIBCLANG_PATH.
-  LIBCLANG_PATH = lib.optionalString withTTS "${llvmPackages.libclang.lib}/lib";
-
-  preBuild = lib.optionalString withTTS ''
-    # When building w/ TTS the speech-dispatcher-sys crate's build.rs uses
-    # rust-bindgen with libspeechd. This bypasses the normal nixpkgs CC wrapper
-    # so we have to adapt the BINDGEN_EXTRA_CLANG_ARGS env var to compensate. See
-    # this blog post[0] for more information.
-    #
-    # [0]: https://hoverbear.org/blog/rust-bindgen-in-nix/
-
-    export BINDGEN_EXTRA_CLANG_ARGS="$(< ${stdenv.cc}/nix-support/libc-cflags) \
-      $(< ${stdenv.cc}/nix-support/cc-cflags) \
-      -isystem ${llvmPackages.libclang.lib}/lib/clang/${
-        lib.getVersion llvmPackages.clang
-      }/include \
-      -idirafter ${stdenv.cc.cc}/lib/gcc/${stdenv.hostPlatform.config}/${
-        lib.getVersion stdenv.cc.cc
-      }/include \
-      -idirafter ${speechd}/include"
-  '';
-
   checkFlags = let
     # Most of Blightmud's unit tests pass without trouble in the isolated
     # Nixpkgs build env. The following tests need to be skipped.