This PR ensures that failure in initial compilation marks the relevant
definitions as `noncomputable`, inside and outside `noncomputable
section`, so that follow-up errors/noncomputable markings are detected
in initial compilation as well instead of somewhere down the pipeline.
This may require additional `noncomputable` markers on definitions that
depend on definitions inside `noncomputable section` but accidentally
passed the new computability check.
Reported at
https://leanprover.zulipchat.com/#narrow/channel/270676-lean4/topic/Cryptic.20error.20message.20in.20new.20lean.20toolchain.3F.
