RFR: 8315061: Make LockingMode a product flag

[Daniel D. Daugherty]

A trivial fix to make LockingMode a product flag.

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Commit messages:
 - 8315061: Make LockingMode a product flag

Changes: https://git.openjdk.org/jdk/pull/15496/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15496&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8315061
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/15496.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15496/head:pull/15496

PR: https://git.openjdk.org/jdk/pull/15496