Print to stderr consistently in bootstrap

[jyn514]

Bootstrap is unfortunately quite inconsistent about which it uses currently :(

$ rg -g '!build.rs' println src/bootstrap/ | grep -v eprintln | wc -l
88
$ rg eprintln src/bootstrap/ | wc -l
60

stderr probably makes more sense? but I don't know when someone would look at just stdout or just stderr; having a hard time imagining use cases.

cc @bjorn3

Originally posted by @jyn514 in #96687 (comment)

[bjorn3]

For example ./x.py test >test_log.txt would show warnings on the terminal as stderr is not redirected but put the results of all tests in test_log.txt. Not that I can recall every doing something like that, but it could be useful I guess.

[jyn514]

Sure, seems fine. Let's use eprintln consistently then.

@rustbot label +E-easy +A-rustbuild

[raiyansayeed]

@rustbot claim

[lionellloh]

@raiyansayeed are you still working on this?

[raiyansayeed]

Hey yes I'm still working on it, have most of it implemented I think. I just haven't gotten the time to review my code / push, although I think I should be able to do it by the end of this week.

[jyn514]

Looks like this was done in #97411, thanks!