Rollup merge of #89756 - jyn514:bootstrap-times, r=Mark-Simulacrum

Rollup merge of #89756 - jyn514:bootstrap-times, r=Mark-Simulacrum

Greatly reduce amount of debuginfo compiled for bootstrap itself

Rather than compiling rustbuild and all its dependencies with
`debuginfo=2`, this compiles dependencies without debuginfo and
rustbuild with `debuginfo=1`. On my laptop, this brings compile times
down from ~1:20 to ~1:05.

See also https://rust-lang.zulipchat.com/#narrow/stream/242791-t-infra/topic/async.20in.20bootstrap.3F/near/254847594.

r? ``@Mark-Simulacrum``