RFR: 8288001: SOURCE_DATE_EPOCH should not be set by default

[Severin Gehwolf]

On Wed, 8 Jun 2022 07:47:24 GMT, KIRIYAMA Takuya <duke at openjdk.java.net> wrote:

> At default configuration, SOURCE_DATE_EPOCH is exported as environment variable in SetupReproducibleBuild. Then, gcc is affected of SOURCE_DATE_EPOCH environment variable. This value is used only to set SOURCE_DATE_ISO_8601 (except below), so I removed "export" for SOURCE_DATE_EPOCH in SetupReproducibleBuild. And, at building ct.sym, SOURCE_DATE_EPOCH environment variable is needed. So I added setting routine if SOURCE_DATE_EPOCH is not set.
> 
> This fix works fine. With default configuration shows -Xinternalversion output same as Windows, and with --with-source-date configuration shows -Xinternalversion output specified timestamp. Would you please review this fix?

It's not clear **why** you don't want `SOURCE_DATE_EPOCH` set by default. Could you explain? It would be good to make the OpenJDK build reproducible by default. The way it works currently, is a first step towards that goal.

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PR: https://git.openjdk.java.net/jdk/pull/9081