Bug 11941: ld.so: Improper assert map->l_init_called in dlclose

Bug 11941: ld.so: Improper assert map->l_init_called in dlclose

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

(cherry picked from commit 57707b7fcc38855869321f8c7827bfe21d729f37)
(cherry picked from commit e9e69e468039fcd57276f783a16aa771a8e4214e)