Fix cpio test in 2038 (#1836)

Fix cpio test in 2038 (#1836)

Without this patch, `bsdcpio_test_option_c` failed after 2038-01-19 with

```
 .../libarchive-3.6.2/cpio/test/test_option_c.c:143: Assertion failed: t >= now - 2
 .../libarchive-3.6.2/cpio/test/test_option_c.c:169: Assertion failed: t >= now - 2
 .../libarchive-3.6.2/cpio/test/test_option_c.c:205: Assertion failed: t >= now - 2
```

Background:
As part of my work on reproducible builds for openSUSE, I check that
software still gives identical build results in the future.
The usual offset is +16 years, because that is how long I expect some
software will be used in some places.
This showed up failing tests in our package build.
See https://reproducible-builds.org/ for why this matters.