libstdc++: optimize EH phase 2

In the ABI's two-phase EH model, first we walk the stack looking for a
handler, then we walk the stack running cleanups until we reach that
handler.  In the cleanup phase, we shouldn't redundantly check the handlers
along the way, e.g. when walking through g():

  void f() { throw 42; }
  void g() { try { f(); } catch (void *) { } }
  int main() { try { g(); } catch (int) { } }

libstdc++-v3/ChangeLog:

	* libsupc++/eh_personality.cc (PERSONALITY_FUNCTION): Don't check
	handlers in the cleanup phase.

libstdc++-v3/libsupc++/eh_personality.cc

@@ -592,6 +592,10 @@ PERSONALITY_FUNCTION (int version,
 	      // Zero filter values are cleanups.
 	      saw_cleanup = true;
 	    }
+	  else if (actions == _UA_CLEANUP_PHASE)
+	    // We checked the handlers in the search phase; if one of them
+	    // matched, actions would also have _UA_HANDLER_FRAME set.
+	    ;
 	  else if (ar_filter > 0)
 	    {
 	      // Positive filter values are handlers.