support for calling Linux syscalls directly

[David Miller]

From: Rich Felker <dalias@aerifal.cx>
Date: Mon, 4 Feb 2013 09:01:27 -0500

> I'm largely against libinux. There does not seem to be any compelling
> reason for making a new library to hold 500 bytes of syscall wrapper
> code, and I agree the distinction of what goes there versus libc seems
> arbitrary and confusing.

This is my position as well, we should just put all the syscall stubs
in libc.