Two minor usnic fixes

* clang warning stomp
* memory barrier for volatile variable use

These can go to 1.7.5 or can slip to v1.8 -- RM decision.

Submitted by Jeff Squyres, reviewed by Dave Goodell

cmr=v1.7.5:reviewer=ompi-rm1.7

This commit was SVN r30944.

ompi/mca/btl/usnic/btl_usnic_cclient.c

@@ -62,6 +62,7 @@ static void client_rml_receive(int status, ompi_process_name_t* sender,
     UNPACK_UINT32(buffer, cddr->udp_port);
 
     /* Tell the main thread that the reply is done */
+    opal_atomic_mb();
     cddr->receive_done = true;
 }
 
@@ -150,6 +151,7 @@ int ompi_btl_usnic_connectivity_listen(ompi_btl_usnic_module_t *module)
     }
 
     /* Get the UDP port number that was received */
+    opal_atomic_mb();
     module->local_addr.connectivity_udp_port = data.udp_port;
 
     return OMPI_SUCCESS;

ompi/mca/btl/usnic/btl_usnic_connectivity.h

@@ -157,11 +157,16 @@ struct ompi_btl_usnic_module_t;
  *
  * Note that this macro will call ompi_btl_usnic_util_abort() if an error
  * occurs.
+ *
+ * Also note that we use a temp variable of the correct type because
+ * some of the values passed in to this macro are volatile, and the
+ * call to opal_dss.unpack() will discard that volatile qualifier.
  */
 #define UNPACK(buffer, type, opal_unpack_type, value)                   \
     do {                                                                \
         int ret_value, n = 1;                                           \
         type temp;                                                      \
+        value = (type) 0;                                               \
         ret_value = opal_dss.unpack((buffer), &temp, &n, opal_unpack_type); \
         if (OPAL_SUCCESS != ret_value) {                                \
             OMPI_ERROR_LOG(ret_value);                                  \