anchor.diff:  { lib, stdenv, fetchurl, zlib, perl }:
   
   let
  +  # check if we can execute binaries for the host platform on the build platform
  +  # even though the platforms aren't the same. mandoc can't be cross compiled
  +  # (easily) because of its configurePhase, but we want to allow “native” cross
  +  # such as pkgsLLVM and pkgsStatic.
  +  executableCross = stdenv.hostPlatform.isCompatible stdenv.buildPlatform;
  +
     # Name of an UTF-8 locale _always_ present at runtime, used for UTF-8 support
     # (locale set by the user may differ). This would usually be C.UTF-8, but
     # darwin has no such locale.
  
positive.code:     PREFIX="$out"
      LD_OHASH="-lutil"
      CC=${stdenv.cc.targetPrefix}cc
      # Bypass the locale(1)-based check for UTF-8 support since it causes trouble:
      # * We only have meaningful locale(1) implementations for glibc and macOS
      # * NetBSD's locale(1) (used for macOS) depends on mandoc
  
negative.code:     printf '%s' "$configureLocal" > configure.local
    '';
  
    doCheck = executableCross;
    checkTarget = "regress";
    checkInputs = [ perl ];
    preCheck = "patchShebangs --build regress/regress.pl";
  