There is at least one use case where during exit a library destructor
might call dlclose() on a valid handle and have it fail with an
assertion. We must allow this case, it is a valid handle, and dlclose()
should not fail with an assert. In the future we might be able to return
an error that the dlclose() could not be completed because the opened
library has already been unloaded and destructors have run as part of
exit processing.
For more details see:
https://www.sourceware.org/ml/libc-alpha/2016-12/msg00859.html
