configure description for brotli/zstd is wrong

From ./configure --help:

[...]
  --without-brotli        disable brotli compression support
  --without-zstd          disable zstd compression support
[...]

But ./configure --without-brotli --without-zstd yields:

configure: WARNING: unrecognized options: --without-brotli, --without-zstd
checking build system type... x86_64-pc-linux-gnu
checking host system type... x86_64-pc-linux-gnu
checking for a BSD-compatible install... /usr/bin/install -c
[...]

In configure.ac, these options are defined as:

AC_ARG_WITH(libbrotli,
	    AS_HELP_STRING([--without-brotli], [disable brotli compression support]),
	    ac_brotli=$withval, ac_brotli=yes)
[...]
AC_ARG_WITH(libzstd,
	    AS_HELP_STRING([--without-zstd], [disable zstd compression support]),
	    ac_zstd=$withval, ac_zstd=yes)
[...]

The first argument of AC_ARG_WITH corresponds to the --{with,without}-* argument, so it all needs to be consistently libbrotli (etc) or brotli (etc).