[compiler-rt] [AIX][PGO] Handle atexit functions when dlclose'ing shared libraries (PR #102940)

[Rainer Orth via llvm-commits]

rorth wrote:

The new `Posix/instrprof-dlopen-norpath.test` test breaks the [Solaris/sparcv9](https://lab.llvm.org/buildbot/#/builders/13/builds/1831) and [Solaris/amd64](https://lab.llvm.org/staging/#/builders/120/builds/1250) buildbots.

https://github.com/llvm/llvm-project/pull/102940