anchor.diff:  
     installPhase = installer nativeB2Args;
   
  -  outputs = [ "out" "lib" ];
  +  outputs = [ "out" "dev" "lib" ];
   
     crossAttrs = rec {
       buildInputs = [ expat.crossDrv zlib.crossDrv bzip2.crossDrv ];
  
positive.code:   withToolset = stdenv.lib.optionalString (toolset != null) "--with-toolset=${toolset}";
  
    genericB2Flags = [
      "--prefix=$out"
      "--libdir=$lib/lib"
      "-j$NIX_BUILD_CORES"
      "--layout=${layout}"
  
negative.code:     # We want to substitute the contents of configureFlags, removing thus the
      # usual --build and --host added on cross building.
      preConfigure = ''
        export configureFlags="--prefix=$dev --without-icu ${concatStringsSep " " commonConfigureFlags}"
        set -x
        cat << EOF > user-config.jam
        using gcc : cross : $crossConfig-g++ ;
  