anchor.diff:  { stdenv, fetchurl, icu, expat, zlib, bzip2, python, fixDarwinDylibNames, libiconv
  +, hostPlatform
   , toolset ? if stdenv.cc.isClang then "clang" else null
   , enableRelease ? true
   , enableDebug ? false
   , enableSingleThreaded ? false
   , enableMultiThreaded ? true
  -, enableShared ? !(stdenv.cross.libc or null == "msvcrt") # problems for now
  +, enableShared ? !(hostPlatform.libc == "msvcrt") # problems for now
   , enableStatic ? !enableShared
   , enablePIC ? false
   , enableExceptions ? false
  
positive.code:     "--user-config=user-config.jam"
      "toolset=gcc-cross"
      "--without-python"
    ] ++ optionals (stdenv.cross.libc == "msvcrt") [
      "target-os=windows"
      "threadapi=win32"
      "binary-format=pe"
      "address-model=${if hasPrefix "x86_64-" stdenv.cross.config then "64" else "32"}"
      "architecture=x86"
    ];
    crossB2Args = concatStringsSep " " (genericB2Flags ++ crossB2Flags);
  
negative.code:     buildPhase = builder crossB2Args;
      installPhase = installer crossB2Args;
      postFixup = fixup;
    } // optionalAttrs (hostPlatform.libc == "msvcrt") {
      patches = fetchurl {
        url = "https://svn.boost.org/trac/boost/raw-attachment/ticket/7262/"
            + "boost-mingw.patch";
  