Spinning off from #51269:

The MIR borrow checker (i.e., NLL) permits #[thread_local] static mut to have 'static lifetime. This is probably a bug. It arises because we ignore borrows of "unsafe places", which includes static mut.

We probably ought to stop doing that — at least not ignoring them entirely — but if we do so, we have to ensure that we continue to accept overlapping borrows of static mut (even though that is basically guaranteed UB), since it compiles today:

fn main() {
 static mut X: usize = 22;
 unsafe {
  let p = &mut X;
  let q = &mut X;
  *p += 1;
  *q += 1;
  *p += 1;
 }
}