Rollup merge of #119451 - Kobzol:ci-pr-clippy, r=Mark-Simulacrum

Gate PR CI on clippy correctness lints

Implements part of rust-lang/compiler-team#709.

Note that `x.py clippy compiler` also checks the standard library, because it needs to be checked before the compiler. This happens even with `x.py clippy --stage 0`.

Author: matthiaskrgr