fixes trac:2355 - race in interaction between opal_atomic_lifo_push

and opal_atomic_lifo_pop. Adds memory barriers to remove the race
condition

This commit was SVN r23014.

The following Trac tickets were found above:
  Ticket 2355 --> https://svn.open-mpi.org/trac/ompi/ticket/2355

opal/include/opal/sys/powerpc/atomic.h

@@ -9,6 +9,7 @@
  *                         University of Stuttgart.  All rights reserved.
  * Copyright (c) 2004-2005 The Regents of the University of California.
  *                         All rights reserved.
+ * Copyright (c) 2010      IBM Corporation.  All rights reserved.
  * $COPYRIGHT$
  * 
  * Additional copyrights may follow
@@ -296,7 +297,6 @@ static inline int32_t opal_atomic_add_32(volatile int32_t* v, int inc)
                         "     add     %0, %2, %0   \n\t"
                         "     stwcx.  %0, 0, %3    \n\t"
                         "     bne-    1b           \n\t"
-                        "     mr      %3, %0       \n\t"
                         : "=&r" (t), "=m" (*v)
                         : "r" (inc), "r" (v), "m" (*v)
                         : "cc");
@@ -314,7 +314,6 @@ static inline int32_t opal_atomic_sub_32(volatile int32_t* v, int dec)
                         "     subf    %0,%2,%0     \n\t"
                         "     stwcx.  %0,0,%3      \n\t"
                         "     bne-    1b           \n\t"
-                        "     mr      %3, %0       \n\t"
                         : "=&r" (t), "=m" (*v)
                         : "r" (dec), "r" (v), "m" (*v)
                         : "cc");