manual: Refactor documentation of CHAR_BIT.

[Joseph Myers]

On Sat, 17 Jun 2017, Zack Weinberg wrote:

> On 06/17/2017 04:42 AM, Rical Jasan wrote:
> > This single-@item @table is better defined with @defvr, since the
> > CHAR_BIT macro has @standards (being declared in a header), and @items
> > in @tables are not considered annotatable.  Using @defvr automatically
> > includes the macro in the Variable and Constant Macro Index and
> > ensures its inclusion the Summary of Library Facilities.
> 
> This part of the change is OK.
> 
> > The file include/limits.h identifies the macro as coming from C99.
> 
> I think this macro really was in C90, and
> http://flash-gordon.me.uk/ansi.c.txt includes it, which is the closest I
> can come to checking.  Joseph, do you know for sure?

CHAR_BIT is C90.

-- 
Joseph S. Myers
joseph@codesourcery.com