time.h and wctype.h had "#error not yet implemented" in them. Now time.h is correct (though the functions
are only declared), and wctype.h exists enough to define its types. Also a dlsym stub was added that just
returns 0.
This commit joins the implementation of exit, _Exit, and abort into a
single translation unit, and also adds atexit, at_quick_exit, and
quick_exit. While this does go against the ideal of all libc functions
being in their own translation unit, their implementations are very
related, and so I think this makes sense.
This new libc is mostly from scratch, with *printf() functions provided
by Marco Paland and Eyal Rozenberg's tiny printf library, and malloc and
friends provided by dlmalloc.
