If we go down this road, I assume there would be a distinction between:
```rust
#[attr] if foo { ... } else { ... } // applies to whole statement, including both branches
```
and 
```rust
if foo #[attr] { ... } else { ... } // only applies to the then-branch
```

I don't have a problem with this; if you cfg-disable a then-branch, you get a compilation error, presumably.  (Though I do think it might motivate support for inner attributes.)