RFR: JDK-8307810: Consistently use LockingMode instead of UseHeavyMonitors [v2]

[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 incrementally with one additional commit since the last revision:

  Dont modify UseHeavyMonitors

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/13900/files
  - new: https://git.openjdk.org/jdk/pull/13900/files/cc8b9fb9..bb805a86

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=13900&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=13900&range=00-01

  Stats: 4 lines in 1 file changed: 0 ins; 4 del; 0 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