devtools: Improve *-check.py tool detection

Summary:
This is important to make sure that we're not testing tools different from the one we're building with.

Introduce determine_wellknown_cmd, which encapsulates how we should handle well-known tools specification (IFS splitting, env override, etc.).

This is a partial backport of core#22381
https://github.com/bitcoin/bitcoin/pull/22381/commits/9fdc8afe117b7b1ea845f8acae9e831922b8f92b

Test Plan: gitian builds

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D13611