[patch] Add preliminary readelf support for ELFCOMPRESS_ZSTD.

[Cary Coutant]

> > This patch adds support to readelf to recognize the new ELF compression
> > type. There is more work to be done to actually support compression and
> > decompression using the zstd library, but I will leave that to the
> > champions of the new compression option.
>
> Okay (if not deemed obvious in the first place), once the ELF side
> change has been committed.

Thanks, committed. (Yeah, I suppose I could have committed under the
trivial and obvious rule.)

-cary