Add override to overriden virtual methods, remove virtual keywords.

No functionality change. Changes made by clang-tidy + some manual cleanup.

llvm-svn: 217028
diff --git a/llvm/lib/Target/ARM/ARMSubtarget.h b/llvm/lib/Target/ARM/ARMSubtarget.h
index 3cbeae8..2fdfc35 100644
--- a/llvm/lib/Target/ARM/ARMSubtarget.h
+++ b/llvm/lib/Target/ARM/ARMSubtarget.h
@@ -437,7 +437,7 @@
 
   /// getInstrItins - Return the instruction itineraries based on subtarget
   /// selection.
-  const InstrItineraryData *getInstrItineraryData() const {
+  const InstrItineraryData *getInstrItineraryData() const override {
     return &InstrItins;
   }