Select assembly sources via preprocessor

[Kojoley]

• Fixes cross-compilation abi and binformat detection.
• abi and binary-format are now optional but can be used to override autodetection.

[olk]

I don't want a big commit containing changes for many different issues - please create one commit for one fix.

[Kojoley]

I don't want a big commit containing changes for many different issues - please create one commit for one fix.

You mean pull request instead of commit? Because currently there is one commit for one thing and I have probably even split it too much.

[Kojoley]

I've removed CI changes from the PR, some of them I've submitted as separate PRs.

[Kojoley]

Ping

[olk]

ty

[olk]

I was forced to revert all you commits because the changes prevented the release (errors on selecting the correct source etc.)

[Kojoley]

I was forced to revert all you commits because the changes prevented the release (errors on selecting the correct source etc.)

It was b2 bug (https://github.com/bfgroup/b2/pull/326), do you interested in trying this again?