cabal-install: add --build-timings flag

[sheaf]

This new flag makes cabal-install dump timing information for the various stages of building a package. This allows us to better see how much time is spending in configure/build stages.

I used this to figure out where we were wasting time for PRs #11767 and #11768. I think it makes sense to add it as a flag so that all users can get better observability (a bit like the -dshow-passes GHC flag).

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[TeofilC]

This looks great to me!

I am currently working on a tool for nicely visualizing module graph build times. I think I could probably be able to use the same tool for visualizing package graph build times.

If this is accepted, then I might make a followup PR to also output this information to a file in dist-newstyle (along with dependency information) and that should work well with my tool

[Mikolaj]

Thank you!

[ulysses4ever]

Thanks for the PR!

I don't want to drag this longer than necessary, but I can't stand asking: how about a machine-readable version of this? Basically, spitting a CSV might be nice. But again it's more of food-for-thought kind of quetsion rather than an actual concern.

[sheaf]

Thanks for the PR!

I don't want to drag this longer than necessary, but I can't stand asking: how about a machine-readable version of this? Basically, spitting a CSV might be nice. But again it's more of food-for-thought kind of quetsion rather than an actual concern.

Yes, that would be nice as well. I think I will let @TeofilC take care of that, given that he has a direct use case for it. I just put up this PR as it's what I was using to benchmark #11768 and #11767 and I thought it might be generally useful.