RFR: 7357: Double-Checked Locking in Agent Plugin code [v3]

[Guru Hb]

> Trivial Fortify warning fix

Guru Hb has updated the pull request incrementally with one additional commit since the last revision:

  fixing LI_LAZY_INIT_STATIC with volatile

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Changes:
  - all: https://git.openjdk.java.net/jmc/pull/282/files
  - new: https://git.openjdk.java.net/jmc/pull/282/files/c9488a1d..2620d3c7

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jmc&pr=282&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jmc&pr=282&range=01-02

  Stats: 4 lines in 1 file changed: 2 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/jmc/pull/282.diff
  Fetch: git fetch https://git.openjdk.java.net/jmc pull/282/head:pull/282

PR: https://git.openjdk.java.net/jmc/pull/282