Fix remaining reproducible builds issues in abuild

[kpcyrd]

• ensures that gzip -n is always used
• normalizes atime and ctime in tar metadata
• explicitly sort the files instead of relying on the order returned by readdir(2)

[mor1]

I haven't been able to test but this looks sensible to me :)
I guess it's too late to merge for the current release though (currently at rc3 I believe).

[kpcyrd]

Sure, I think it was already to late to merge when I wrote this patch. :)

We're currently using an abuild with this patch applied at https://tests.reproducible-builds.org/alpine/alpine.html

[algitbot]

Merged in 660f793, 4f5b0a1 by @ncopa. Thanks for your contribution!

(This pull request has been closed automatically by GitHub PR Closer. If you think that it’s not resolved yet, please add a comment.)

[ncopa]

merged with 660f793 and 4f5b0a1. thanks!