libctf: improving the compressor, optionally-available algorithms

[Nick Alcock]

On 5 Feb 2021, Matthias Klose stated:

> On 2/5/21 5:38 PM, Nick Alcock wrote:
>> On 5 Feb 2021, Matthias Klose said:
>>> On 2/5/21 1:17 PM, Nick Alcock via Binutils wrote:
>>>> To anyone concerned: does this seem sensible? Is it actually totally
>>>> impractical to assume that anything other than zlib is available ever?
>>>> (I hope not).
>>>
>>> GCC currently supports zstd for it's streaming format, and what I know from
>>> compressing distro packages, zstd is faster for decompressing with slightly
>>> bigger compressed data.
>> 
>> Hm, bigger compressed data than *zlib*? That's rather surprising to me.
>> Oh well.
>
> sorry, no, a little bigger than xz.

Oh right, that's what I was assuming, one reason why I suggested it as
the default compressor (if available) rather than xz -- well, that and
the *compression* speed, since the compression penalty is paid whenever
anyone links something, whether the .ctf is ever used at all. I really
don't want to slow down the linker.