These need to get their safety story straight

This previously failed on Windows because the `llvm_config` file was
open as read-only.

…tgross35

Make more Windows functions `#![deny(unsafe_op_in_unsafe_fn)]`

As part of rust-lang#127747, I've evaluated some more Windows functions and added `unsafe` blocks where necessary. Some are just trivial wrappers that "inherit" the full unsafety of their function, but for others I've added some safety comments. A few functions weren't actually unsafe at all. I think they were just using `unsafe fn` to avoid an `unsafe {}` block.

I'm not touching `c.rs` yet because that is partially being addressed by another PR and also I have plans to further reduce the number of wrapper functions we have in there.

r? libs

Prevent double reference in generic futex

In the Windows futex implementation we were a little lax at allowing references to references (i.e. `&&`) which can lead to deadlocks due to reading the wrong memory address. This uses a trait to tighten the constraints and ensure this doesn't happen.

r? libs

Reviewer on vacation

``@jhpratt`` asked to be set as on vacation

…onur-ozkan

bootstrap: open `llvm-config` as r+w

This previously failed on Windows and prevented building on Windows for compiler stuff because the `llvm-config` file was open as read-only.

Tested locally on a Windows machine.

Fixes rust-lang#127849.