Related to #5777 but a separate issue:
Please allow specifying rustflags per profile.
It would be very useful for setting certain flags only in debug or release (or even custom profiles).

E.g. I have a workspace with multiple crates, plus one backend bin crate and one frontend wasm crate, and I want to set rustflags = ["-Ctarget-feature=+crt-static", "-Ctarget-cpu=haswell"] only for the backend and only for release builds!
Btw, when I just set rustflags = ["-Ctarget-feature=+crt-static", "-Ctarget-cpu=haswell"] in .cargo/config now, (even though rustc ignores these flags when building my wasm frontend), cargo always recompiles all deps when switching between building the backend and frontend sub-crates. Even though for the frontend, everything is compiled for the wasm target anyway, so the compiled deps are never shared between frontend and backend crates! (Probably avoidable / another issue.)

If it was possible to set rustflags per profile, together with profile-overrides it would be possible to avoid the unnecessary recompilation because I could set rustflags only for the backend and only for release builds, and in addition I could set other flags only for the frontend crate.

Also this would allow things like using the standard linker for release and lld for debug builds (to shorten linking time).