RFR: 8293584: CodeCache::old_nmethods_do incorrectly filters is_unloading nmethods

[Coleen Phillimore]

I fixed the code to also include is_unloading nmethods.  I couldn't write a dedicated test for this.
Tested with tier1-4,6.  Also tried to reproduce another redefinition bug with this change, which didn't reproduce, but not caused by this change.

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Commit messages:
 - 8293584: CodeCache::old_nmethods_do incorrectly filters is_unloading nmethods

Changes: https://git.openjdk.org/jdk/pull/11243/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11243&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8293584
  Stats: 5 lines in 1 file changed: 0 ins; 4 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/11243.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11243/head:pull/11243

PR: https://git.openjdk.org/jdk/pull/11243