RFR: JDK-8297242: Use-after-free during library unloading on Linux

[Justin King]

ASan identified a use-after-free in `os::dll_unload` caused by referencing memory owned by the dynamic loader after closing the library.

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Commit messages:
 - Use ifdef/endif block instead of LINUX_ONLY
 - Add missing semicolon
 - Merge branch 'openjdk:master' into dll-heap-use-after-free
 - Fix use-after-free during library unloading on Linux

Changes: https://git.openjdk.org/jdk/pull/11231/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11231&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8297242
  Stats: 15 lines in 1 file changed: 12 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/11231.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11231/head:pull/11231

PR: https://git.openjdk.org/jdk/pull/11231