I seem to be taking a wrong turn somewhere. Running find . -type f -print0 | xargs -0 /bin/grep D_FMT in /usr/include for the installed 1.1.4 yields:
./langinfo.h:#define D_FMT 0x20029
./langinfo.h:#define ERA_D_FMT 0x2002E

Pulling the latest sources and running the same command in gitdir yields:
./src/time/strptime.c: s = strptime(s, nl_langinfo(D_FMT), tm);
./src/time/strftime.c: item = D_FMT;
./include/langinfo.h:#define D_FMT 0x20029
./include/langinfo.h:#define ERA_D_FMT 0x2002E

Neither directory yields a result for DATE_FMT. Am I botching the unix-fu, barking up the wrong tree or something else entirely?

On Thu, Aug 14, 2014 at 3:46 PM, Rich Felker <dalias@libc.org> wrote:

On Thu, Aug 14, 2014 at 03:31:23PM -0400, Alec Salazar wrote:
> Is there any interest or plan to support the xopen xpg4 standard? My
> specific interest is regarding zfs on linux. There is a function call
> nl_langinfo(_DATE_FMT). Apparently this nl item was added in xpg4. I'm
> wondering what the possibility is of a long-term solution.

_DATE_FMT is just an incorrect or obsolete spelling for DATE_FMT. The
latter is standard and is supported by musl.

Rich