strftime() _GNU_SOURCE extension request

[Vito Caputo]

Hello list,

I'd like to propose a _GNU_SOURCE extension for strftime() treating
str=NULL similarly to snprintf()'s C99 handling of str=NULL; write
nothing to str, but return the number of bytes that /would/ be written
if str were non-NULL and sufficiently large.

Thanks,
Vito Caputo