Add _Unwind_Action to unwind-arm.h.  This wasn't originally needed, but is now
because it is explicitly referenced by the function that is shared between the
two ObjC personality functions.

Patch by Emmanuel Maillard!



git-svn-id: svn+ssh://svn.gna.org/svn/gnustep/libs/libobjc2/trunk@36315 72102866-910b-0410-8b05-ffd578937521