RFR: JDK-8307810: Consistently use LockingMode instead of UseHeavyMonitors [v4]

[Thomas Stuefe]

> [JDK-8291555](https://bugs.openjdk.org/browse/JDK-8291555) phased out UseHeavyMonitors in favor of LockingMode=0. We forgot to apply these changes to PPC and S390. 
> 
> Since UseHeavyMonitors implies LockingMode, but not vice versa, we now have a mismatch if JVM is started with LockingMode=0 but without UseHeavyMonitors. That leads to crashes.
> 
> The patch fixes that, and in addition makes sure that if LockingMode=0 is set, we are setting UseHeavyMonitors too.

Thomas Stuefe 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. The pull request contains four additional commits since the last revision:

 - Merge branch 'openjdk:master' into JDK-8307810-use-lockingmode-instead-of-useheavymonitors
 - Merge branch 'master' into JDK-8307810-use-lockingmode-instead-of-useheavymonitors
 - Dont modify UseHeavyMonitors
 - JDK-8307810-use-lockingmode-instead-of-useheavymonitors

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/13900/files
  - new: https://git.openjdk.org/jdk/pull/13900/files/af7dab6c..dc870294

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=13900&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=13900&range=02-03

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/13900.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13900/head:pull/13900

PR: https://git.openjdk.org/jdk/pull/13900