RFR: 8347840: Fix testlibrary compilation warnings [v3]

[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:

  revert change

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/23143/files
  - new: https://git.openjdk.org/jdk/pull/23143/files/6a23012e..7a1c35da

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=23143&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=23143&range=01-02

  Stats: 4 lines in 1 file changed: 2 ins; 2 del; 0 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