__register_atfork
implements
pthread_atfork
as specified in ISO/IEC 9945:2003 Portable Operating System(POSIX)and The Single UNIX® Specification(SUS) V3.
The additional parameter __dso_handle allows a shared
object to pass in it's handle so that functions registered by
__register_atfork
can be unregistered by the runtime when
the shared object is unloaded.