Add <compare> backport

[AntoinePrv]

Checklist

• [x] The title and the commit message(s) are descriptive
• [x] Small commits made to fix your PR have been squashed to avoid history pollution
• [x] Tests have been added for new features or bug fixes
• [x] API of new functions and classes are documented

Description

A backport of the C++20 header for integer comparison.

[JohanMabille]

@AntoinePrv can you rebase you PR on master please? Everything shoud be green after.

[AntoinePrv]

Could be nice to experiment with a rebase action e.g. https://github.com/marketplace/actions/automatic-rebase

[JohanMabille]

indeed!