RFR: 8238650: Allow to override buildDate with SOURCE_DATE_EPOCH

Wed Apr 14 12:32:19 UTC 2021

On Mon, 8 Mar 2021 17:32:20 GMT, John Neffenger <jgneff at openjdk.org> wrote:

>> Long term, yes.
>> 
>> I am currently low on time and my Java-foo is not that great, so I was hoping that someone would pick it up.
>
>> I am currently low on time and my Java-foo is not that great, so I was hoping that someone would pick it up.
> 
> @bmwiedemann Thank you for getting this important change started. If you can finish this pull request, I'll follow up with some additional changes to support reproducible builds. Otherwise, if you're still short on time, I can pick up where you left off. So far I managed to create reproducible Java artifacts — all but the native shared libraries (and the `javafx.graphics.jmod` file that includes them).

@jgneff feel free to pick it up.

When linking shared libraries, ensure that .o files are listed in deterministic order - i.e. `sort(glob(*.c))` and check if individual .c or .o files vary between builds.

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