[SystemZ] Remove "virtual" from override methods

Also fix a couple of cases where "override" was missing.  No behavioural
change intended.

llvm-svn: 203110
diff --git a/llvm/lib/Target/SystemZ/SystemZSubtarget.h b/llvm/lib/Target/SystemZ/SystemZSubtarget.h
index fbb89ef..ffca2d8 100644
--- a/llvm/lib/Target/SystemZ/SystemZSubtarget.h
+++ b/llvm/lib/Target/SystemZ/SystemZSubtarget.h
@@ -43,7 +43,7 @@
                    const std::string &FS);
 
   // This is important for reducing register pressure in vector code.
-  virtual bool useAA() const override { return true; }
+  bool useAA() const override { return true; }
 
   // Automatically generated by tblgen.
   void ParseSubtargetFeatures(StringRef CPU, StringRef FS);