enabling a only a single lint is not intuitive

[matthiaskrgr]

https://rust-lang.zulipchat.com/#narrow/stream/131828-t-compiler/topic/.E2.9C.94.20silencing.20all.20but.20one.20rustc.20lint

I wanted to do a simple task: silence all but one particular rustc lint.
rustc -Awarnings "allows" all the warnings, easy so we only need to re-warn a single lint:
rustc -Awarnings -Wdead-code
As it turns out this does not work, -Awarnings does silence all lints, even the ones enabled again after the flag (order does not matter it seems).
Similar thing works just fine with clippy: clippy-driver -Aclippy::all -Wclippy::redundant_clone only warns about redundant clones`

I found out I can archive this for rustc by passing force-warn with every lint manually, so
rustc/clippy-driver -Awarnings --force-warn dead-code --force-warn clippy::redundant_clone but this is kinda horribly UX imo.

Can we just make -Awarnings -Wunused_variables work intuitively?