logic_bug lint should understand `cfg!`

[ipetkov]

Had a use case where a certain input parameter must trigger some fallback behavior for a specific OS, but clippy reported it as a logical bug:

let v: Vec<_> = ...;

if cfg!(windows) && v.is_empty() {
   // fallback behavior
} else {
   // default behavior for Unix/non-empty param
}

Clippy is correctly reporting that this is equivalent to false && ... on unix systems, but removing the first check (as per the suggestion) does not reflect the actual programmer intent

[oli-obk]

Dupe of #1885

Rustc isn't telling us about macros anymore... we can't do much on our end

[llogiq]

Is there a rustic bug about this?

[oli-obk]

rust-lang/rust#43268