(needs_initialization): Declare it as volatile so we get proper memory

ordering when accessing it.  Also, shrink size to 1 byte and move
	it closer to other frequently-used fields.

(Logical change 1.121)

include/tdep-ia64.h

@@ -163,9 +163,10 @@ struct cursor
 
 struct ia64_global_unwind_state
   {
-    int needs_initialization;
     pthread_mutex_t lock;		/* global data lock */
 
+    volatile char needs_initialization;
+
     /* Table of registers that prologues can save (and order in which
        they're saved).  */
     const unsigned char save_order[8];