[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/SystemZElimCompare.cpp b/llvm/lib/Target/SystemZ/SystemZElimCompare.cpp
index 6cee9c2..fdf80a9 100644
--- a/llvm/lib/Target/SystemZ/SystemZElimCompare.cpp
+++ b/llvm/lib/Target/SystemZ/SystemZElimCompare.cpp
@@ -66,7 +66,7 @@
   SystemZElimCompare(const SystemZTargetMachine &tm)
     : MachineFunctionPass(ID), TII(0), TRI(0) {}
 
-  virtual const char *getPassName() const {
+  const char *getPassName() const override {
     return "SystemZ Comparison Elimination";
   }