Document strftime %Ob and %OB as C2X features

  C2X standardizes strftime %Ob and %OB support.  This patch updates the
glibc manual to say these are C2X features.

Note: C2X seems unclear to me about whether %h being equivalent to %b
means %Oh is thereby allowed and equivalent to %Ob; I've asked WG14.

Tested with "make info" and "make pdf".

2019-08-15  Joseph Myers  <joseph@codesourcery.com>

	* manual/time.texi (strftime): Document %Ob and %OB as C2X
	features.
  

* Joseph Myers:

> C2X standardizes strftime %Ob and %OB support.  This patch updates the
> glibc manual to say these are C2X features.
>
> Note: C2X seems unclear to me about whether %h being equivalent to %b
> means %Oh is thereby allowed and equivalent to %Ob; I've asked WG14.
>
> Tested with "make info" and "make pdf".
>
> 2019-08-15  Joseph Myers  <joseph@codesourcery.com>
>
> 	* manual/time.texi (strftime): Document %Ob and %OB as C2X
> 	features.
>
> diff --git a/manual/time.texi b/manual/time.texi
> index bfa46dd45b..aeb24382ea 100644
> --- a/manual/time.texi
> +++ b/manual/time.texi
> @@ -1352,7 +1352,7 @@ alternative numeric symbols.
>  With @code{%B}, @code{%b}, and @code{%h}: use the grammatical form for
>  month names that is appropriate when the month is named by itself,
>  rather than the form that is appropriate when the month is used as
> -part of a complete date.  This is a GNU extension.
> +part of a complete date.  This is a C2X feature.
>  @end table
>  
>  If the format supports the modifier but no alternative representation
> @@ -1372,13 +1372,13 @@ The full weekday name according to the current locale.
>  @item %b
>  The abbreviated month name according to the current locale, in the
>  grammatical form used when the month is part of a complete date.
> -As a GNU extension, the @code{O} modifier can be used (@code{%Ob})
> +As a C2X feature, the @code{O} modifier can be used (@code{%Ob})
>  to get the grammatical form used when the month is named by itself.
>  
>  @item %B
>  The full month name according to the current locale, in the
>  grammatical form used when the month is part of a complete date.
> -As a GNU extension, the @code{O} modifier can be used (@code{%OB})
> +As a C2X feature, the @code{O} modifier can be used (@code{%OB})
>  to get the grammatical form used when the month is named by itself.
>  
>  Note that not all languages need two different forms of the month

C2X (in the form of N2385) is ambiguous on the relative meaning of %B
and %OB, so the precise meaning defined in the manual is still a GNU
extension.  Not sure if that matters.  I do not have objection to this
patch.

Thanks,
Florian