anchor.diff:  }:
   let
   
  -  prebuilt_crt = {
  +  choosePlatform =
  +    let pname = stdenv.targetPlatform.parsed.cpu.name; in
  +    pset: pset.${pname} or (throw "bionic-prebuilt: unsupported platform ${pname}");
  +
  +  prebuilt_crt = choosePlatform {
       aarch64 = fetchzip {
         url =  "https://android.googlesource.com/platform/prebuilts/gcc/linux-x86/aarch64/aarch64-linux-android-4.9/+archive/98dce673ad97a9640c5d90bbb1c718e75c21e071/lib/gcc/aarch64-linux-android/4.9.x.tar.gz";
         sha256 = "sha256-LLD2OJi78sNN5NulOsJZl7Ei4F1EUYItGG6eUsKWULc=";
  
positive.code:       sha256 = "sha256-y7CFLF76pTlj+oYev9taBnL2nlT3+Tx8c6wmicWmKEw=";
        stripRoot = false;
      };
    }.${stdenv.targetPlatform.parsed.cpu.name};
  
    prebuilt_libs = {
      aarch64 = fetchzip {
        url = "https://android.googlesource.com/platform/prebuilts/ndk/+archive/f2c77d8ba8a7f5c2d91771e31164f29be0b8ff98/platform/platforms/android-30/arch-arm64/usr/lib.tar.gz";
        sha256 = "sha256-TZBV7+D1QvKOCEi+VNGT5SStkgj0xRbyWoLH65zSrjw=";
  
negative.code:       sha256 = "sha256-XEd7L3cBzn+1pKfji40V92G/uZhHSMMuZcRZaiKkLnk=";
        stripRoot = false;
      };
    };
  
    ndk_support_headers = fetchzip {
      url ="https://android.googlesource.com/platform/prebuilts/clang/host/linux-x86/+archive/0e7f808fa26cce046f444c9616d9167dafbfb272/clang-r416183b/include/c++/v1/support.tar.gz";
  