Subzero: Use more "= default;" for ctors and dtors.

src/IceTargetLoweringMIPS32.h

Index: src/IceTargetLoweringMIPS32.h
diff --git a/src/IceTargetLoweringMIPS32.h b/src/IceTargetLoweringMIPS32.h
index 5383f38196a2c17ee03eae4024cd0e72516da765..eb4a9fd282b1c5d68d6a85cd6c9c6813612eaa3a 100644
--- a/src/IceTargetLoweringMIPS32.h
+++ b/src/IceTargetLoweringMIPS32.h
@@ -124,7 +124,7 @@ protected:
   static IceString RegNames[];
 
 private:
-  ~TargetMIPS32() override {}
+  ~TargetMIPS32() override = default;
 };
 
 class TargetDataMIPS32 final : public TargetDataLowering {
@@ -145,7 +145,7 @@ protected:
   explicit TargetDataMIPS32(GlobalContext *Ctx);
 
 private:
-  ~TargetDataMIPS32() override {}
+  ~TargetDataMIPS32() override = default;
   template <typename T> static void emitConstantPool(GlobalContext *Ctx);
 };