Fix xlc warning: typeof.

Author: awlauria

opal/include/opal/sys/arm64/atomic_llsc.h

@@ -23,6 +23,11 @@
  * $HEADER$
  */
 
+#if defined(__xlC__) || defined(__IBMC__) || defined(__IBMCPP__) || defined(__ibmxl__)
+/* Silence -Wlanguage-extension-token */
+#define typeof __typeof__
+#endif
+
 #if !defined(OPAL_SYS_ARCH_ATOMIC_LLSC_H)
 
 #define OPAL_SYS_ARCH_ATOMIC_LLSC_H