guestfs-tools: patch less shebangs

pkgs/tools/virtualization/guestfs-tools/default.nix

@@ -66,16 +66,16 @@ stdenv.mkDerivation rec {
     xz
   ];
 
+  preConfigure = ''
+    patchShebangs ocaml-dep.sh.in ocaml-link.sh.in run.in
+  '';
+
   makeFlags = [
     "LIBGUESTFS_PATH=${libguestfs-with-appliance}/lib/guestfs"
   ];
 
   enableParallelBuilding = true;
 
-  preBuild = ''
-    patchShebangs .
-  '';
-
   postInstall = ''
     wrapProgram $out/bin/virt-win-reg \
       --prefix PERL5LIB : ${with perlPackages; makeFullPerlPath [ hivex libintl-perl libguestfs-with-appliance ]}