RFR: 8238650: Allow to override buildDate with SOURCE_DATE_EPOCH

[Kevin Rushforth]

On Thu, 27 Feb 2020 00:01:28 GMT, Kevin Rushforth <kcr at openjdk.org> wrote:

>> Allow to override buildDate 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 PR was done while working on reproducible builds for openSUSE.
>
> Finally getting to this (sorry for the delay). This seems OK to me, as it is not an intrusive change. I do not think
> that actually setting this property for production builds is a good idea, so I recommend against that (ultimately that
> will be up to Gluon or whoever produces builds).  I'll test it once you change it from an env variable to a gradle
> property.

@bmwiedemann are you planning to pursue this PR?

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PR: https://git.openjdk.java.net/jfx/pull/99