request: properly connect cargo check and cargo build

[crlf0710]

Currently cargo check and cargo build works in isolate. A much better way is get them connected. So that:

• After a successful cargo build, a cargo check should pick up the incremental build data, and finish (almost) immediately without doing real work.
• After a successful cargo check, a cargo build should pick up the incremental build data, and continue to do the codegen part, instead of starting from scratch.

[varkor]

Previously reported at #50037. cargo issue: rust-lang/cargo#3501.

[crlf0710]

#50037 is about rustbuild so that's different...at least on the surface.

This is the same as cargo#3501 though. But i feel this is actually a rustc problem with incremental build and metadata format in the root. And it's more visible in this repo :) Maybe i should not close it as duplicate.