RFR: 8347840: Fix testlibrary compilation warnings [v2]

[Leonid Mesnik]

> There few compiler warning disabled in the testlibary build.
> They should be fixed or localized and removed from build to prevent new possible issues.
> 
> The main goal is to avoid new such issues in the testlibrary. 
> Tested with tier1-5 to ensure that all tests were passed.

Leonid Mesnik has updated the pull request incrementally with one additional commit since the last revision:

  fixed comments

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/23143/files
  - new: https://git.openjdk.org/jdk/pull/23143/files/ae302c9c..6a23012e

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=23143&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=23143&range=00-01

  Stats: 52 lines in 10 files changed: 6 ins; 42 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/23143.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23143/head:pull/23143

PR: https://git.openjdk.org/jdk/pull/23143