Re-commit r247216: "Fix Clang-tidy misc-use-override warnings, other minor fixes"

Except the changes that defined virtual destructors as =default, because that
ran into problems with GCC 4.7 and overriding methods that weren't noexcept.

llvm-svn: 247298
diff --git a/llvm/lib/CodeGen/MIRPrintingPass.cpp b/llvm/lib/CodeGen/MIRPrintingPass.cpp
index 13d61e6..8e7566a 100644
--- a/llvm/lib/CodeGen/MIRPrintingPass.cpp
+++ b/llvm/lib/CodeGen/MIRPrintingPass.cpp
@@ -40,7 +40,7 @@
     MachineFunctionPass::getAnalysisUsage(AU);
   }
 
-  virtual bool runOnMachineFunction(MachineFunction &MF) override {
+  bool runOnMachineFunction(MachineFunction &MF) override {
     std::string Str;
     raw_string_ostream StrOS(Str);
     printMIR(StrOS, MF);
@@ -48,7 +48,7 @@
     return false;
   }
 
-  virtual bool doFinalization(Module &M) override {
+  bool doFinalization(Module &M) override {
     printMIR(OS, M);
     OS << MachineFunctions;
     return false;