[jdk18u] RFR: 8278525: Additional -Wnonnull errors happen with GCC 11

[Aleksey Shipilev]

Clean backport for GCC 11 compatibility.

Additional testing:
 - [x] Linux x86_64 fastdebug build with GCC 9

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Commit messages:
 - Backport 6eb6ec05fd4f80e11d0b052b58190bc8b53f4b11

Changes: https://git.openjdk.org/jdk18u/pull/152/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk18u&pr=152&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8278525
  Stats: 5 lines in 1 file changed: 5 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk18u/pull/152.diff
  Fetch: git fetch https://git.openjdk.org/jdk18u pull/152/head:pull/152

PR: https://git.openjdk.org/jdk18u/pull/152