ssdeep: only run patchelf on linux

pkgs/tools/security/ssdeep/default.nix

@@ -9,9 +9,11 @@ stdenv.mkDerivation rec {
     sha256 = "1igqy0j7jrklb8fdlrm6ald4cyl1fda5ipfl8crzyl6bax2ajk3f";
   };
 
+  buildInputs = stdenv.lib.optional (!stdenv.isDarwin) [ patchelf ];
+
   # For some reason (probably a build system bug), the binary isn't
   # properly linked to $out/lib to find libfuzzy.so
-  postFixup = ''
+  postFixup = stdenv.lib.optionalString (!stdenv.isDarwin) ''
     rp=$(patchelf --print-rpath $out/bin/ssdeep)
     patchelf --set-rpath $rp:$out/lib $out/bin/ssdeep
   '';