anchor.diff:  
   # Make sure we get GNU sed.
   assert stdenv.isDarwin -> gnused != null;
  +
  +# Need c++filt on darwin
  +assert stdenv.isDarwin -> binutils != null;
   
   # The go frontend is written in c++
   assert langGo -> langCC;
  
positive.code:     # The builder relies on GNU sed (for instance, Darwin's `sed' fails with
      # "-i may not be used with stdin"), and `stdenvNative' doesn't provide it.
      ++ (optional stdenv.isDarwin gnused)
      ;
  
    NIX_LDFLAGS = stdenv.lib.optionalString  stdenv.isSunOS "-lm -ldl";
  
negative.code: , libpthread ? null, libpthreadCross ? null  # required for GNU/Hurd
  , stripped ? true
  , gnused ? null
  , binutils ? null
  }:
  
  assert langJava     -> zip != null && unzip != null
  