anchor.diff: -{ lib, stdenv, cmake, fetch, libcxx, llvm, version
  -, standalone ? false
  +{ lib, stdenv, cmake, fetch, libcxx, libunwind, llvm, version
  +, standalone ? stdenv.hostPlatform.useLLVM or false
     # on musl the shared objects don't build
   , enableShared ? !stdenv.hostPlatform.isStatic
   }:
  
positive.code:   src = fetch "libcxxabi" "1zcqxsdjhawgz1cvpk07y3jl6fg9p3ay4nl69zsirqb2ghgyhhb2";
  
    nativeBuildInputs = [ cmake ];
  
    postUnpack = ''
      unpackFile ${libcxx.src}
  
negative.code:     patch -p1 -d $(ls -d libcxx-*) -i ${../../libcxx-0001-musl-hacks.patch}
    '';
  
    cmakeFlags = lib.optionals standalone [
      "-DLLVM_ENABLE_LIBCXX=ON"
      "-DLIBCXXABI_USE_LLVM_UNWINDER=ON"
    ] ++ lib.optional (!enableShared) "-DLIBCXXABI_ENABLE_SHARED=OFF";
  
    installPhase = if stdenv.isDarwin
      then ''
  