include: make APK packing mtime reproducible

include: make APK packing mtime reproducible

APK kindly stores the mtime of each containing file in created packages,
breaking reproducibility. As a fix, touch all files of the package with the
timestamp of PKGSOURCE_DATE_EPOCH, which contains the timestamp based on the
last package modification.

Over at OPKG, something similar is done by setting mtime in the tar command,
see the `ipkg-build` script.

To tackle this in APK directly, some changes are suggested. However until this
is merged, we should fix it downstream.
https://gitlab.alpinelinux.org/alpine/apk-tools/-/merge_requests/348

Signed-off-by: Paul Spooren <mail@aparcar.org>