Allow to override build date with SOURCE_DATE_EPOCH

Description

Applies a patch from Bernhard Wiedemann, from the OpenSUSE team, that makes the builds reproducible:

https://reproducible-builds.org/

API Changes and Justification

Backwards Compatible Changes

• This change introduces no API changes
• This change adds new API calls

Backwards Incompatible Changes

• This change modifies an existing API
• This change removes an existing API

If any of the Backwards Incompatible check boxes are ticked please provide a justification why this change is necessary and why it needs to be done in a backwards incompatible way.

Review Status

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