RHEL7.5 ships a libldap backed by OpenSSL instead of NSS. This may mitigate the concurrency issues which drove us to libldap_r. This suggests that libldap.so may be viable again. However, it may not advertise the thread safety flags which we rely upon to enable or disable global synchronization around libldap calls.
We should investigate whether we can dynamically detect the underlying TLS implementation underneath libldap, and use that information to toggle synchronization.