fortify-headers: fix inconsistent time_t version of ppoll

fortify-headers: fix inconsistent time_t version of ppoll

Bug:
fortify/poll.h includes poll.h, which redirects ppoll to __ppoll_time64
if the _REDIR_TIME64 macro is 1. Then fortify/poll.h will #undef ppoll
and use the 32 bit version.

Fix: we should not do this when _REDIR_TIME64 is 1.

[1] https://forum.openwrt.org/t/idle-cpu-usage-of-usbmuxd/140331/15
[2] https://github.com/openwrt/openwrt/issues/12574

Signed-off-by: Georgi Valkov <gvalkov@gmail.com>