[jdk15u-dev] RFR: 8251549: Update docs on building for Git

Tue Apr 6 15:29:38 UTC 2021

jdk15u is in process of migrating to Git (jdk15u-dev is already there), so we would need a variant of this document in 15u, too.
This exact patch applies clean.
Yes, clean with some chunks shifted the uniform  42 lines. These lines, it seems to me, belong mostly to updates JDK-8256182 and JDK-8247591 and are irrelevant to this task.

I have plan for making building.html as a separate task  -- a backport of JDK-8257224 if possible but maybe not.

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Commit messages:
 - Backport 042734cc5b17302a8f2ecdf577511bd6d5ec5e22

Changes: https://git.openjdk.java.net/jdk15u-dev/pull/18/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk15u-dev&pr=18&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8251549
  Stats: 68 lines in 1 file changed: 12 ins; 37 del; 19 mod
  Patch: https://git.openjdk.java.net/jdk15u-dev/pull/18.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk15u-dev pull/18/head:pull/18

PR: https://git.openjdk.java.net/jdk15u-dev/pull/18