Don't always alias

[eyalroz]

At the moment, the library always aliases printf, sprintf, vsprintf etc. This is problematic, because you might want to use it alongside the standard library's <stdio.h> (whether because you're using the standard library as well, or because you're including another header which itself pulls <stdio.h> without you really needing it).

So, we should have a CMake option controlling whether or not this is done.