RFR: 8308286 Fix clang warnings in linux code [v5]

[Artem Semenov]

> When using the clang compiler to build OpenJDk on Linux, we encounter various "warnings as errors".
> They can be fixed with small changes.

Artem Semenov has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains five commits:

 - update
 - update
 - update
 - update
 - 8308286 Fix clang warnings in linux code

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Changes: https://git.openjdk.org/jdk/pull/14033/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=14033&range=04
  Stats: 16 lines in 6 files changed: 14 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/14033.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14033/head:pull/14033

PR: https://git.openjdk.org/jdk/pull/14033