Could you explain more about why you'd need to port things? If you have a libc, shouldn't it "just work"? Do you have to scatter #define or #ifdef all over? What about if you wanted to support Golang? Would you have to implement a bunch of syscall?

Well, the LibC is still quite small, and the syscalls aren't really compatible with Linux. A lot of things to port, for example Vim, require system libraries such as ncurses which need syscalls that aren't in the LibC. I don't really need many #ifdefs, at least not for most things, as it's a more or less posix-based libc.