This corrects the `span_with_body` in the case of closures, which was
incorrectly shortened to the `def_span`.

Reimplement `carrying_add` and `borrowing_sub` for signed integers.

As per the discussion in rust-lang#85532, this PR reimplements `carrying_add` and `borrowing_sub` for signed integers.

It also adds unit tests for both unsigned and signed integers, emphasing on the behaviours of the methods.

Compute information about function parameters on THIR

This avoids some manipulation of typeck results while building MIR.

Avoid UB in the Windows filesystem code in... bootstrap?

This basically a subset of the changes from rust-lang#101171. I didn't think to look in src/bootstrap for more windows filesystem API usage, which was apparently a mistake on my part. It's kinda goofy that stuff like this is in here, but what are you gonna do, computers are awful.

I also added `winbase` to the `winapi` dep -- I tested this in a tmp crate but needed to add this to your Cargo.toml -- you `use winapi::stuff::winbase` in this function, but are relying on something else turning on that feature.