The mkdir(2) function returns 0 on success, and -1 on error.
This resolves an error in TestIoDevice when /tmp/.device/ does not
exist.
Bug: https://bugs.gentoo.org/635838
* shell: add missing NULL checks
* thread: handle case where HAVE_EVENTFD_H isn't defined
* wlog: return NULL instead of 0
* wlog: use g_RootLog instead of WLog_GetRoot
otherwise a new root might be initialized on uninit
* indentation and style fixes