LZ4 enabled by default since 7c1849311e49

Hi all,
(Added in CC buildfarm owners of animals that I know are already
failing.)

Since 7c1849311e49, LZ4 has been enabled by default in the builds on
HEAD.  Like ICU or readline, this can be overridden with the addition
of a --without-lz4 to disable the library.  If possible, I would
recommend adding a package like lz4-devel or equivalent so as builds
are able to work.

Sorry for the inconvenience.

Thanks,
--
Michael