scummvm: add support for FluidSynth

This gives by far the best music and general sound quality for games
with MIDI support.

pkgs/games/scummvm/default.nix

···
-{ stdenv, nasm
-, fetchurl, SDL2, SDL2_net, freetype, zlib, libmpeg2, libjpeg, libmad, libogg, libvorbis, flac, alsaLib, mesa
+{ stdenv, fetchurl, nasm
+, alsaLib, flac, fluidsynth, freetype, libjpeg, libmad, libmpeg2, libogg, libvorbis, mesa, SDL2, zlib
 , hostPlatform
 }:
 
···
   nativeBuildInputs = [ nasm ];
 
   buildInputs = [
-    SDL2 SDL2_net
-    freetype libjpeg libmpeg2 libmad libogg libvorbis flac alsaLib mesa zlib
+    alsaLib freetype flac fluidsynth libjpeg libmad libmpeg2 libogg libvorbis mesa SDL2 zlib
   ];
 
   enableParallelBuilding = true;