[jdk21u-dev] RFR: 8316907: Fix nonnull-compare warnings

[SendaoYan]

Hi all,
There are some gcc compile warnings which recorded by [JDK-8342304](https://bugs.openjdk.org/browse/JDK-8342304), and the PR [JDK-8316893](https://bugs.openjdk.org/browse/JDK-8316893) fix the gcc compile warnings. So I want to backport [JDK-8316893](https://bugs.openjdk.org/browse/JDK-8316893) to jdk21u-dev. But before backport [JDK-8316893](https://bugs.openjdk.org/browse/JDK-8316893), we should backport [JDK-8316907](https://bugs.openjdk.org/browse/JDK-8316907) first, [JDK-8316907](https://bugs.openjdk.org/browse/JDK-8316907) solve  nonnull-compare warnings emitted by GCC after removing `-fno-delete-null-pointer-checks`.

Additional testing:

1. jtreg tests(include tier1/2/3 etc.) with linux-x64 release build
2. jtreg tests(include tier1/2/3 etc.) with linux-x64 fastdebug build
3. jtreg tests(include tier1/2/3 etc.) with linux-aarch64 release build
4. jtreg tests(include tier1/2/3 etc.) with linux-aarch64 fastdebug build

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Commit messages:
 - Backport 516cfb135f7e5fefaf6e6f2928f6ecb88806f1ef

Changes: https://git.openjdk.org/jdk21u-dev/pull/1172/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=1172&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8316907
  Stats: 6 lines in 2 files changed: 0 ins; 6 del; 0 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/1172.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/1172/head:pull/1172

PR: https://git.openjdk.org/jdk21u-dev/pull/1172