Allow to override build date with SOURCE_DATE_EPOCH

[bmwiedemann]

Allow to override build date with SOURCE_DATE_EPOCH
in order to make builds reproducible.
See https://reproducible-builds.org/ for why this is good
and https://reproducible-builds.org/specs/source-date-epoch/
for the definition of this variable.

This date call only works with GNU date.

Without this patch, I got such diff:

/usr/lib64/libnvidia-container.so.1.1.1 differs in ELF section .rodata
@@ -106,8 +106,8 @@
  13650 73656c66 2f6e732f 25730073 7472696e  self/ns/%s.strin
  13660 6720666f 726d6174 74696e67 20666169  g formatting fai
  13670 6c656400 312e312e 31007665 7273696f  led.1.1.1.versio
- 13680 6e3a2025 730a0032 3032302d 30362d32  n: %s..2020-06-2
- 13690 34543136 3a35332b 30303a30 30006275  4T16:53+00:00.bu
+ 13680 6e3a2025 730a0032 3033352d 30372d32  n: %s..2035-07-2
+ 13690 38543036 3a30392b 30303a30 30006275  8T06:09+00:00.bu
  136a0 696c6420 64617465 3a202573 0a006275  ild date: %s..bu

And with the patch, we can do bit-reproducible package builds of libnvidia-container.

This PR was done while working on reproducible builds for openSUSE.

[bmwiedemann]

I'd still like to see this merged. Is there anything left to do? Something I can help with?

[elezar]

Hello There!

Thanks for your contribution!
This repository is a read-only mirror of the following repository: https://gitlab.com/nvidia/container-toolkit/libnvidia-container

Do you mind:

• Opening a pull request against that repo?
• Making sure your work is signed: https://help.github.com/en/github/authenticating-to-github/signing-commits

Thanks again!

(sorry for the delay in responding. Our bot that should have responded automatically was down for a bit)

[bmwiedemann]

forwarded to https://gitlab.com/nvidia/container-toolkit/libnvidia-container/-/merge_requests/47