anchor.diff:  { fetchurl, lib, stdenv, buildPackages
   , curl, openssl, zlib, expat, perlPackages, python3, gettext, cpio
   , gnugrep, gnused, gawk, coreutils # needed at runtime by git-filter-branch etc
  -, openssh, pcre2
  +, openssh, pcre2, bash
   , asciidoc, texinfo, xmlto, docbook2x, docbook_xsl, docbook_xml_dtd_45
   , libxslt, tcl, tk, makeWrapper, libiconv
   , svnSupport, subversionClient, perlLibs, smtpPerlLibs
  
positive.code:   NIX_LDFLAGS = lib.optionalString (stdenv.cc.isGNU && stdenv.hostPlatform.libc == "glibc") "-lgcc_s"
                + lib.optionalString (stdenv.isFreeBSD) "-lthr";
  
    configureFlags = lib.optionals (stdenv.buildPlatform != stdenv.hostPlatform) [
      "ac_cv_fread_reads_directories=yes"
      "ac_cv_snprintf_returns_bogus=no"
      "ac_cv_iconv_omits_bom=no"
      "ac_cv_prog_CURL_CONFIG=${curl.dev}/bin/curl-config"
    ];
  
    preBuild = ''
  
negative.code:   nativeBuildInputs = [ gettext perlPackages.perl makeWrapper ]
      ++ lib.optionals withManual [ asciidoc texinfo xmlto docbook2x
           docbook_xsl docbook_xml_dtd_45 libxslt ];
    buildInputs = [ curl openssl zlib expat cpio libiconv bash ]
      ++ lib.optionals perlSupport [ perlPackages.perl ]
      ++ lib.optionals guiSupport [tcl tk]
      ++ lib.optionals withpcre2 [ pcre2 ]
  