Auto merge of #148035 - bjorn3:check_skip_codegen_crate, r=madsmtm

Skip codegen_crate call in check mode

This way we don't have to spawn the coordinator thread. Some errors will no longer be emitted with this in check mode. For example the check that `-Ctarget-cpu` is passed on targets that need this.

Suggested by `@saethlin`

Author: bors