anchor.diff:  , sslSupport ? false, openssl ? null
   , gnutlsSupport ? false, gnutls ? null
   , scpSupport ? false, libssh2 ? null
  -, gssSupport ? false, gss ? null
  +, gssSupport ? false, kerberos ? null
   , c-aresSupport ? false, c-ares ? null
   }:
   
  
positive.code: assert gnutlsSupport -> gnutls != null;
  assert scpSupport -> libssh2 != null;
  assert c-aresSupport -> c-ares != null;
  
  stdenv.mkDerivation rec {
    name = "curl-7.56.0";
  
negative.code:       ( if idnSupport then "--with-libidn=${libidn.dev}" else "--without-libidn" )
      ]
      ++ stdenv.lib.optional c-aresSupport "--enable-ares=${c-ares}"
      ++ stdenv.lib.optional gssSupport "--with-gssapi=${kerberos}";
  
    CXX = "c++";
    CXXCPP = "c++ -E";
  