RFR: JDK-8320830: Dont mix os::dll_load() with direct dlclose() calls

[Joachim Kern]

We should not mix os::dll_load() with dlclose(), but should call os::dll_unload(). At the moment this is benign, but this prevents certain type of platforms specific workarounds inside os::dll_load() and is a prerequisite for these upcoming changes. 

There are two places I see where this happens, both are AIX specific:


os/aix/libodm_aix.cpp
51: dlclose(_libhandle);
58: if (_libhandle) { dlclose(_libhandle); }

os/aix/libperfstat_aix.cpp
117: dlclose(g_libhandle);

-------------

Commit messages:
 - JDK-8320830

Changes: https://git.openjdk.org/jdk/pull/16846/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16846&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8320830
  Stats: 3 lines in 2 files changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/16846.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16846/head:pull/16846

PR: https://git.openjdk.org/jdk/pull/16846