RFR: 8342042: PPC64: compiler_fast_unlock_object flags failure instead of success [v2]

[Richard Reingruber]

> This change inverts the `EQ` bit in `flag` with a condition register nand instruction in order to meet the post condition given at L2751-L2752:
> 
> 
>   // flag == EQ indicates success, decrement held monitor count
>   // flag == NE indicates failure
> 
> 
> The fix passed our CI testing with LockingMode set to LM_LEGACY
> Tier1-4 of hotspot and jdk. All of Langtools and jaxp. Renaissance Suite and SAP specific tests.
> Testing was done on the main platforms and also on Linux/PPC64le and AIX.
> 
> The test runtime/logging/MonitorInflationTest.java failed on all platforms. Apparently it has issues with LM_LEGACY.

Richard Reingruber has updated the pull request incrementally with one additional commit since the last revision:

  Same enhancement for compiler_fast_unlock_lightweight_object as suggested by Axel

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/21496/files
  - new: https://git.openjdk.org/jdk/pull/21496/files/1963e884..b24743a9

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=21496&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=21496&range=00-01

  Stats: 11 lines in 1 file changed: 2 ins; 6 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/21496.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21496/head:pull/21496

PR: https://git.openjdk.org/jdk/pull/21496