Get libffi closures to cope with SELinux execmem/execmod

[Andrew Haley]

Andrew Haley writes:
 > 
 > When a Java object, such as a Class, is being finalized, it is
 > reachable.  So, disposing of the closures at this point is potentially
 > dangerous.  Please disable the call to
 > _Jv_ClosureList::releaseClosures for the time being, and we'll
 > investigate ways to defer the release until the class in unreachable.
 > I know this will cause a small memory leak, but we'll live with that
 > for the time being.  (One idea I have is to mark the closures as dead,
 > and then have a separate loop that reclaims them after all finalizers
 > have run.)

Or, alterntatively, we'll be able to prove that my worries here are
unfounded, and we'll put the call back in.

Andrew.