anchor.diff:      buildPhase = builder crossB2Args;
       installPhase = installer crossB2Args;
       postFixup = fixup;
  +  } // optionalAttrs stdenv.isCrossWin {
  +    patches = fetchurl {
  +      url = "https://svn.boost.org/trac/boost/raw-attachment/ticket/7262/"
  +          + "boost-mingw.patch";
  +      sha256 = "0s32kwll66k50w6r5np1y5g907b7lcpsjhfgr7rsw7q5syhzddyj";
  +    };
  +
  +    patchFlags = "-p0";
     };
   }
  
positive.code:   ] ++ optionals stdenv.isCrossWin [
      "target-os=windows"
      "threadapi=win32"
    ];
    crossB2Args = concatStringsSep " " (genericB2Flags ++ crossB2Flags);
  
  
negative.code: { stdenv, fetchurl, icu, expat, zlib, bzip2, python, fixDarwinDylibNames
  , toolset ? if stdenv.cc.isClang then "clang" else null
  , enableRelease ? true
  , enableDebug ? false
  