4lDO2

Possible UB since preadv accepts &[IoVec<&mut [u8]>]

2

In Rust, attempting to obtain a mutable reference from an immutable reference is immediately Undefined Behavior, unless UnsafeCell is used, which includes mutable references behind immutable references (`&&mut [u8]`, or...

Fixes https://github.com/mozilla/cbindgen/issues/891. I made this configurable, but I'm not sure if that's correct. Should `...` be the default, or only accepted translation, given Rust supports both `va: ...` and `va:...