Rollup merge of #143707 - Kobzol:bootstrap-std-check, r=jieyouxu

Fix `--skip-std-check-if-no-download-rustc`

Since rust-lang/rust#143048, we now explicitly set the build compiler for `check::Std`, which caused it to be built before we checked `--skip-std-check-if-no-download-rustc`. So I moved the check earlier to `make_run`, which resolves it.

I also added a regression test for this. Sadly we can't really test for the positive case easily (when download-ci-rustc is enabled), but we can test the negative cases, where it is disabled.

Fixes: rust-lang/rust#143705

r? ```@RalfJung```

Author: tgross35