[PATCH] manual: Update the _ISOC99_SOURCE description.

[Rical Jasan]

On 02/19/2018 08:15 AM, Joseph Myers wrote:
> On Mon, 19 Feb 2018, Rical Jasan wrote:
> 
>> The current description refers to ISO C99 not being widely adopted,
>> which it is believed to be now.
>>
>> 	* manual/creature.texi (_ISOC99_SOURCE): Update the dated
>> 	description.
> 
> OK.

Committed; e8d190b9ed81

Thanks,
Rical