Rollup merge of #145252 - shepmaster:demote-x86_64-apple-darwin-to-tier-2, r=Kobzol,madsmtm

Demote x86_64-apple-darwin to Tier 2 with host tools

Switch to only using aarch64 runners (implying we are now cross-compiling) and stop running tests. In the future, we could enable (some?) tests via Rosetta 2.

This implements the decision from rust-lang/rfcs#3841.

Author: jhpratt