Fix _XOPEN_SOURCE problem on DragonFly
Fix _XOPEN_SOURCE problem on DragonFly

As on FreeBSD, defining _XOPEN_SOURCE to 600 on DragonFly BSD 2.4-RELEASE
or later hides symbols from programs, which leads to implicit declaration
of functions, making the return value to be assumed an int.  On architectures
where sizeof(int) < sizeof(void *), this can cause unexpected behaviors or
crashes.
This change won't affect other OSes unless they define __DragonFly__ macro,
or older versions of DragonFly BSD as the current git code doesn't rely on
the features only available with _XOPEN_SOURCE set to 600 on DragonFly.

Signed-off-by: YONETANI Tomokazu <cde1a2cdc64ce71e8be9bce4516471842192a22a@dragonflybsd.org>
Signed-off-by: Junio C Hamano <a6723cc3f76163bf7adb636a73ac3b0ceb3e6b9b@pobox.com>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git