RFR: 8300696 : [AIX] AttachReturnError fails

[Deepa Kumari]

AttachReturnError.java fails because "VM.dynlibs" prints a list of loaded dynamic libs referring to a cache. The cache may contain stale entries related to unloaded libraries (libReturnError.so in this case). Reloading this cache after unloading libraries solves the problem.

Reported Issue : [JDK-8300696](https://bugs.openjdk.org/browse/JDK-8300696)

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Commit messages:
 - 8300696 : [AIX] AttachReturnError fails

Changes: https://git.openjdk.org/jdk/pull/12138/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12138&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8300696
  Stats: 5 lines in 1 file changed: 5 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/12138.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12138/head:pull/12138

PR: https://git.openjdk.org/jdk/pull/12138