[jdk16] RFR: 8258380: [JVMCI] don't clear InstalledCode reference when unloading JVMCI nmethods

[Tom Rodriguez]

Moved to the JDK16 repo from https://github.com/openjdk/jdk/pull/1777  cc @fisk

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Commit messages:
 - 8258380: [JVMCI] don't clear InstalledCode reference when unloading JVMCI nmethods

Changes: https://git.openjdk.java.net/jdk16/pull/25/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk16&pr=25&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8258380
  Stats: 7 lines in 2 files changed: 6 ins; 1 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk16/pull/25.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk16 pull/25/head:pull/25

PR: https://git.openjdk.java.net/jdk16/pull/25