RFR: JDK-8320830: [AIX] Dont mix os::dll_load() with direct dlclose() calls [v2]

[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);

Joachim Kern has updated the pull request incrementally with one additional commit since the last revision:

  replaced local scope by class scope

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/16846/files
  - new: https://git.openjdk.org/jdk/pull/16846/files/cb3df4fb..b1ce5764

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=16846&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=16846&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 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