Fix minor portability warning on macOS

[embray]

I've noticed the macOS build is generating a few compile-time warnings that I don't see on Linux.

Just minor warnings that shouldn't likely have any runtime effect, from what I'm seeing, but I still think any warnings look unprofessional and should either be dealt with or explicitly silenced.

Should have a look at these.

[embray]

Looks like I already fixed a few of those. There's still a handful other minor warnings, some of them not unique to MacOS