gitAndTools.diff-so-fancy: Fix shebang patching and clean up

perl is a runtime dependency so it needs to be in buildInputs,
otherwise patchShebangs hook will not see it.

pkgs/applications/version-management/git-and-tools/diff-so-fancy/default.nix

@@ -11,12 +11,19 @@ stdenv.mkDerivation rec {
     sha256 = "0aavxahzha2mms4vdwysk79pa6wzswpfwgsq2hwaxnaf66maahfl";
   };
 
-  # Perl is needed here for patchShebangs
-  nativeBuildInputs = [ perl makeWrapper ];
+  nativeBuildInputs = [
+    makeWrapper
+  ];
 
-  buildPhase = null;
+  buildInputs = [
+    perl # needed for patchShebangs
+  ];
+
+  dontBuild = true;
 
   installPhase = ''
+    runHook preInstall
+
     mkdir -p $out/bin $out/lib/diff-so-fancy
 
     # diff-so-fancy executable searches for it's library relative to
@@ -32,6 +39,8 @@ stdenv.mkDerivation rec {
       --prefix PATH : "${git}/bin" \
       --prefix PATH : "${coreutils}/bin" \
       --prefix PATH : "${ncurses.out}/bin"
+
+    runHook postInstall
   '';
 
   meta = with stdenv.lib; {