[throwawaylinux]

You can if you are careful what you use libc for, of course you can't use most of its process management, threading, or make any reentrancy or thread safety assumptions.

I don't mean you would be likely use it if you were writing a normal application in C, but a special case like creating your own runtime where existing interfaces don't do exactly what you like. You wouldn't be using those things in libc anyway in that case.