Rollup merge of #143577 - Noratrieb:Noratrieb-patch-4, r=Kobzol

Disable download-rustc for library profile

The feature currently completely breaks `x test` (rust-lang/rust#142505), core functionality of working on the standard library. Therefore it should be disabled by default until that problem is fixed. Having to wait a bit longer for a check build is nothing compared to completely mysterious build errors when testing.

Author: jieyouxu