RFR: 8264449: Enable reproducible builds with SOURCE_DATE_EPOCH [v7]

[John Neffenger]

On Tue, 6 Dec 2022 18:32:19 GMT, Johan Vos <jvos at openjdk.org> wrote:

> Speaking of which, that is my main worry about this PR: we are increasing our dependency on Gradle by adding logic inside the build.gradle file.

You mean the 17-line `setFileTimestamps` method? I see that as the main issue, as all the other changes are trivial or just clean-up tasks: removing incorrect uses of tabs in Makefiles and finally fixing old `FIXME` notes, for example.

The `setFileTimestamps` method actually removes a dependency on Gradle by setting the timestamps in a way that's consistent with the JDK itself, Apache Maven, and even Apache Ant. I was reluctant to add it, but it's the best solution I found to Kevin's review asking me **not** to use the hard-coded timestamps implemented by Gradle.

As I implied in my message to the mailing list, this is the pull request that frees us from Gradle.

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PR: https://git.openjdk.org/jfx/pull/446