Implement memory barriers

xtoskrnl/includes/i686/ari.h

@@ -59,6 +59,10 @@ XTCDECL
 VOID
 ArLoadTaskRegister(USHORT Source);
 
+XTCDECL
+VOID
+ArMemoryBarrier();
+
 XTCDECL
 ULONG_PTR
 ArReadControlRegister(IN USHORT ControlRegister);
@@ -83,6 +87,10 @@ XTCDECL
 ULONGLONG
 ArReadTimeStampCounter();
 
+XTCDECL
+VOID
+ArReadWriteBarrier();
+
 XTAPI
 VOID
 ArSetGdtEntryBase(IN PKGDTENTRY Gdt,