Allow `-A`, `-W` and `-D` in `x.py clippy` arguments

[Milo123459]

Currently, you cannot pass those CLI flags to x.py clippy. It would be useful if this was possible.

[matthiaskrgr]

you can add them to the args vec in src/bootstrap/check.rs:46, that will work temporarily

[Milo123459]

Ah, thanks for letting me know. I still think that allowing support for these flags is a good idea though.