snd: 20.3 -> 21.1; broaden platforms; parallelize

Also updated the homepage URL.

Upstream has removed GTK support in favour of motif (I know!).

snd's README mentions a bunch of supported Unix platforms, so
constraining this to just Linux is wrong.

pkgs/applications/audio/snd/default.nix

@@ -1,30 +1,30 @@
 { lib, stdenv, fetchurl, pkg-config
-, gtk2, alsaLib
-, fftw, gsl
+, alsaLib, fftw, gsl, motif, xorg
 }:
 
 stdenv.mkDerivation rec {
-  name = "snd-20.3";
+  pname = "snd";
+  version = "21.1";
 
   src = fetchurl {
-    url = "mirror://sourceforge/snd/${name}.tar.gz";
-    sha256 = "016slh34gb6qqb38m8k9yg48rbhc5p12084szcwvanhh5v7fc7mk";
+    url = "mirror://sourceforge/snd/snd-${version}.tar.gz";
+    sha256 = "1jxvpgx1vqa6bwdzlzyzrjn2swjf9nfhzi9r1r96ivi0870vvjk3";
   };
 
   nativeBuildInputs = [ pkg-config ];
 
-  buildInputs = [
-    gtk2 alsaLib
-    fftw gsl
-  ];
+  buildInputs = [ alsaLib fftw gsl motif ]
+    ++ (with xorg; [ libXext libXft libXpm libXt ]);
 
-  meta = {
-    description = "Sound editor";
-    homepage = "http://ccrma.stanford.edu/software/snd";
-    platforms = lib.platforms.linux;
-    license = lib.licenses.free;
-    maintainers = with lib.maintainers; [ ];
-  };
+  configureFlags = [ "--with-motif" ];
 
+  enableParallelBuilding = true;
 
+  meta = with lib; {
+    description = "Sound editor";
+    homepage = "https://ccrma.stanford.edu/software/snd/";
+    platforms = platforms.unix;
+    license = licenses.free;
+    maintainers = with maintainers; [ ];
+  };
 }