[Rpm-maint] [rpm-software-management/rpm] Enable thread autodetection for a parallel compression. (#1324)

[marxin]

Thank you for your thoughts.

Let's first summarize what tricks are done for `xz`:
https://github.com/rpm-software-management/rpm/blob/28b3704034a9c772959485a130b918f414da9796/rpmio/rpmio.c#L811-L859

- the compression supports `%{_xz_memlimit}` limit
- for 32-bit it calculates how much memory will be used based on `lzma_stream_encoder_mt_memusage`

The logic seems to me very complex :) and I'm curious if it counts with a fact that multiple `rpm` files are compressed in parallel?
`zstd` does have a similar function for memory usage, but not available for multi-threaded mode:
https://github.com/facebook/zstd/issues/2232

I see the biggest challenge in the concurrent runs. About the 32-bit targets: from SUSE perspective we don't case much as we can happily use non-threaded mode for them. 


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