RFR: 8134630: make code and comments consistent for stack lock optimization

[Daniel D.Daugherty]

Comment only changes copied from the 'arm' version to the aarch64 and x86
versions of the files. I looked at the ppc and s390 files and it wasn't at all clear
to me how to apply the same comment changes to those platforms.

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Commit messages:
 - 8134630: make code and comments consistent for stack lock optimization

Changes: https://git.openjdk.java.net/jdk/pull/1210/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=1210&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8134630
  Stats: 42 lines in 2 files changed: 36 ins; 0 del; 6 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1210.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1210/head:pull/1210

PR: https://git.openjdk.java.net/jdk/pull/1210