Use CHANGES file date instead of build date

[bmwiedemann]

in order to make builds reproducible.
See https://reproducible-builds.org/ for why this is good

Alternative patches could use $SOURCE_DATE_EPOCH as described in
https://wiki.debian.org/ReproducibleBuilds/TimestampsProposal#Bash_.2F_POSIX_shell

[codecov]

Codecov Report

Merging #15 into master will decrease coverage by 0.02%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master      #15      +/-   ##
==========================================
- Coverage   18.08%   18.06%   -0.03%     
==========================================
  Files           4        4              
  Lines        2206     2209       +3     
==========================================
  Hits          399      399              
- Misses       1807     1810       +3

Impacted Files	Coverage Δ
gap/interact.gi	14.16% <0%> (-0.04%)	⬇️
gap/general.gi	19.75% <0%> (ø)	⬆️

[fingolfin]

While I do think reproducible builds are a good thing, the patch proposed here is not acceptable, nor is using SOURCE_DATE_EPOCH or any other non-portable GNU rxtensions.

However, I think we could simply stop putting the date there; seems not very useful anyway. I will look into it.

[bmwiedemann]

Yes, it should work on BSD date, too - just not Solaris and the like. So dropping the date is indeed a good option. Would even simplify the overall code.

[bmwiedemann]

Hi, any progress on this? Is there something I can help with? (in September after vacations)

[fingolfin]

Merged #16 instead