anchor.diff:  { stdenv, lib, buildPackages
   , autoreconfHook, texinfo, fetchurl, perl, xz, libiconv, gmp ? null
  +, openssl ? null
   , hostPlatform, buildPlatform
   , aclSupport ? false, acl ? null
   , attrSupport ? false, attr ? null
  
positive.code:     ];
  
  
    buildInputs = [ gmp ]
      ++ optional aclSupport acl
      ++ optional attrSupport attr
      ++ optionals hostPlatform.isCygwin [ autoreconfHook texinfo ]   # due to patch
  
negative.code: 
    # Saw random failures like ‘help2man: can't get '--help' info from
    # man/sha512sum.td/sha512sum’.
    enableParallelBuilding = true;
  
    NIX_LDFLAGS = optionalString selinuxSupport "-lsepol";
    FORCE_UNSAFE_CONFIGURE = optionalString hostPlatform.isSunOS "1";
  