Add --quiet flag to x.py and bootstrap to suppress output

[erickt]

This adds a --quiet flag to x.py and bootstrap to suppress some of the output when compiling Rust. It works by passing the flag down to the underlying cargo, cmake, ninja, or make processes.

[rustbot]

This PR modifies src/bootstrap/src/core/config.

If appropriate, please update CONFIG_CHANGE_HISTORY in src/bootstrap/src/utils/change_tracker.rs.

This PR changes how LLVM is built. Consider updating src/bootstrap/download-ci-llvm-stamp.

[rustbot]

r? @Mark-Simulacrum

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[jieyouxu]

I can only look into these this weekend, but cc also #154587

(It would be nice to be careful that we don't use --quiet to mean different things)

[erickt]

Ha! What a coincidence. I’m certainly intending to have the same semantics as that PR, so I think they should be compatible with each other. I’m happy to wait for it to land since it beat me by a few hours, then I can match the style with whatever you finalize on.

[jieyouxu]

(I think either one can land first, I was just remarking just in case we somehow have --quiet do two entirely different things which would be very confusing, but doesn't seem like the case)