enable 64-bit time_t support

Since the code enforces a max time which is getting close to y2038,
enable 64-bit time_t support to avoid overflows.

BUG=b:307794426
TEST=CQ passes

Change-Id: I13b63b7b85e06d9bf21e4030f6483f6255ab54e4
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/tlsdate/+/4978698
Tested-by: Mike Frysinger <vapier@chromium.org>
Auto-Submit: Mike Frysinger <vapier@chromium.org>
Commit-Queue: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Pavol Marko <pmarko@chromium.org>
Commit-Queue: Pavol Marko <pmarko@chromium.org>
1 file changed