WIP: Add speedup_options cache

[singiamtel]

Checking which options are available is expensive, this way we only do it once (as the git available in path is not expected to change during execution)

Follow up to https://github.com/alisw/alibuild/pull/849#issuecomment-2176100822

• [ ] Check if there's any situation where this breaks (e.g. we construct the cache with the host machine's git, and then try to use unsupported flags from docker)

[singiamtel]

Closed this accidentally when managing my own fork