anchor.diff:    # As zlib takes part in the stdenv building, we don't want references
     # to the bootstrap-tools libgcc (as uses to happen on arm/mips)
     NIX_CFLAGS_COMPILE = stdenv.lib.optionalString (!stdenv.isDarwin) "-static-libgcc";
  -
  -  postInstall = stdenv.lib.optionalString stdenv.isDarwin ''
  -    # jww (2015-01-06): Sometimes this library install as a .so, even on
  -    # Darwin; others time it installs as a .dylib.  I haven't yet figured out
  -    # what causes this difference.
  -    for file in $out/lib/*.so* $out/lib/*.dylib* ; do
  -      install_name_tool -id "$file" $file
  -    done
  -  '';
   
     crossAttrs = {
       dontStrip = static;
  
positive.code:     description = "Lossless data-compression library";
      license = licenses.zlib;
    };
  }
  
negative.code: 
  let version = "1.2.8"; in
  
  stdenv.mkDerivation (rec {
    name = "zlib-${version}";
  
    src = fetchurl {
  