- use rustix version of sigwinch signal
- add a lifetime to FileDesc and replace FileDesc::Static to
  FileDesc::Borrowed. This made it necessary to either add a lifetime to
  the libc version of FileDesc or replace all the callers with multiple
  paths (libc, rustix). Changing FileDesc was more straightforward.
  There are no usages of FileDesc found in any repo on github, so this
  change should be reasonably safe.