RFR: 8278766: Enable OpenJDK build support for reproducible jars and jmods using --date

[Andrew Leonard]

If "reproducible build" is enabled, then utilize the new --date option in the building of jar's and jmods.
Validating the boot jdk supports --date for the building of the jars.

Signed-off-by: Andrew Leonard <anleonar at redhat.com>

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Commit messages:
 - 8278766: Enable OpenJDK build support for reproducible jars and jmods using --date

Changes: https://git.openjdk.java.net/jdk/pull/6878/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6878&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8278766
  Stats: 55 lines in 6 files changed: 40 ins; 3 del; 12 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6878.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6878/head:pull/6878

PR: https://git.openjdk.java.net/jdk/pull/6878