Add <limits.h> integer width macros

[Joseph Myers]

On Sat, 17 Sep 2016, Florian Weimer wrote:

> Anyway, Bool has padding bits with GCC, so the remark quoted above is
> technically wrong.  This can be seen with this code

I've added "other than @code{_Bool}" to the documentation in the patch I 
committed.

-- 
Joseph S. Myers
joseph@codesourcery.com