[feat] Add membarrier system call

Also, change the signature of maxine_cache_flush to Address. Doing so avoids
upcasting to Pointer when we have an Address and we don't need the enhanced
functionality of Pointer over Address at this point anyway.

com.sun.max/src/com/sun/max/vm/MaxineVM.java

@@ -592,7 +592,13 @@ public static void registerCriticalMethod(CriticalMethod criticalEntryPoint) {
      * @param length the number of instructions * sizeof one instruction
      */
     @C_FUNCTION
-    public static native void maxine_cache_flush(Pointer start, int length);
+    public static native void maxine_cache_flush(Address start, int length);
+
+    /**
+     * Executes a membarrier(2) system call on Linux systems.
+     */
+    @C_FUNCTION
+    public static native void syscall_membarrier();
 
     @C_FUNCTION
     public static native long arithmeticldiv(long x, long y);