Make the build reproducible

[lamby]

Whilst working on the Reproducible Builds effort I noticed that tpm2-pytss could not be built reproducibly.

This is due to the documentation embedding the current build date. This PR results in the build system using a date seeded from the SOURCE_DATE_EPOCH environment variable... if it exists.

I originally filed this in Debian as bug #1022777.

[williamcroberts]

Please sign off your commit to make the DCO bot happy.

Are the docs considered part of the tpm2-pytss package on Debian? I couldn't find any existing packages.

[lamby]

Are the docs considered part of the tpm2-pytss package on Debian? I couldn't find any existing packages.

Yes. Look for the python-tpm2-pytss-doc package. :)

(Added the sign-off line..)

[williamcroberts]

Are the docs considered part of the tpm2-pytss package on Debian? I couldn't find any existing packages.

Yes. Look for the python-tpm2-pytss-doc package. :)

Would it be better to get the year of last commit from git or would requiring git for the build be an issue?

[codecov]

Codecov Report

Merging #376 (164ab37) into master (b4d3763) will increase coverage by 0.39%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #376      +/-   ##
==========================================
+ Coverage   88.41%   88.80%   +0.39%     
==========================================
  Files          18       18              
  Lines        6394     6394              
  Branches      979      828     -151     
==========================================
+ Hits         5653     5678      +25     
+ Misses        605      583      -22     
+ Partials      136      133       -3     

Impacted Files	Coverage Δ
src/tpm2_pytss/encoding.py	92.42% <0.00%> (+2.28%)	⬆️

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[lamby]

Would it be better to get the year of last commit from git or would requiring git for the build be an issue?

GIt (the .git/ directory and the git binaries themselves) are not guaranteed to be around for a build, no.