[jdk11u-ri] RFR: 8210008: custom extension for make/SourceRevision.gmk [v2]

[Erik Joelsson]

> Backporting this to 11.0.0.1 RI release to facilitate a clean backport of [JDK-8210283](https://bugs.openjdk.org/browse/JDK-8210283) which among other things adapts the source revision build logic for Git. The patch applies cleanly and only touches the source revision build logic.

Erik Joelsson has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase.

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Changes:
  - all: https://git.openjdk.org/jdk11u-ri/pull/3/files
  - new: https://git.openjdk.org/jdk11u-ri/pull/3/files/a5529241..a5529241

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk11u-ri&pr=3&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk11u-ri&pr=3&range=00-01

  Stats: 0 lines in 0 files changed: 0 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk11u-ri/pull/3.diff
  Fetch: git fetch https://git.openjdk.org/jdk11u-ri pull/3/head:pull/3

PR: https://git.openjdk.org/jdk11u-ri/pull/3