Fixing a bunch of -Woverloaded-virtual warnings due to hiding getSubtargetImpl from the base class. NFC.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@218050 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Target/Hexagon/HexagonTargetMachine.h

@@ -31,6 +31,7 @@ public:
                        Reloc::Model RM, CodeModel::Model CM,
                        CodeGenOpt::Level OL);
 
+  using LLVMTargetMachine::getSubtargetImpl;
   const HexagonSubtarget *getSubtargetImpl() const override {
     return &Subtarget;
   }