Implement KeGetCurrentProcessorNumber() routine

xtoskrnl/includes/amd64/kei.h

@@ -21,6 +21,10 @@ XTAPI
 PKPROCESSOR_CONTROL_BLOCK
 KeGetCurrentProcessorControlBlock(VOID);
 
+XTAPI
+ULONG
+KeGetCurrentProcessorNumber(VOID);
+
 XTAPI
 PKTHREAD
 KeGetCurrentThread(VOID);