perl: don't use libxcrypt on FreeBSD

      optional crossCompiling "mini";

    setOutputFlags = false;

    propagatedBuildInputs = lib.optional enableCrypt libxcrypt;

    # On FreeBSD, if Perl is built with threads support, having

    # libxcrypt available will result in a build failure, because

    # perl.h will get conflicting definitions of struct crypt_data

    # from libc's unistd.h and libxcrypt's crypt.h.

    #

    # FreeBSD Ports has the same issue building the perl port if

    # the libxcrypt port has been installed.

    #

    # Without libxcrypt, Perl will still find FreeBSD's crypt functions.

    propagatedBuildInputs = lib.optional (enableCrypt && !stdenv.isFreeBSD) libxcrypt;

    disallowedReferences = [ stdenv.cc ];