RFR: 8253034: Update symbol generation to accomodate Git as the SCM [v2]

[Joe Darcy]

> The symbol generation script assumed Mercurial was being used as the SCM. This should now be updated to Git.

Joe Darcy has updated the pull request incrementally with one additional commit since the last revision:

  Respond to review feedback

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/161/files
  - new: https://git.openjdk.java.net/jdk/pull/161/files/2910def1..c577063c

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=161&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=161&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/161.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/161/head:pull/161

PR: https://git.openjdk.java.net/jdk/pull/161