[jdk11u-dev] RFR: 8308286: Fix clang warnings in linux code

[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.

As in the original patch, I added instructions to the make to suppress the clang compiler warnings.

@djelinski please review

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Commit messages:
 - Backport 98a954eebc4f97dd16cb89bd4f1122952c8482ca

Changes: https://git.openjdk.org/jdk11u-dev/pull/2016/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk11u-dev&pr=2016&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8308286
  Stats: 13 lines in 9 files changed: 8 ins; 0 del; 5 mod
  Patch: https://git.openjdk.org/jdk11u-dev/pull/2016.diff
  Fetch: git fetch https://git.openjdk.org/jdk11u-dev.git pull/2016/head:pull/2016

PR: https://git.openjdk.org/jdk11u-dev/pull/2016