[X86] Set isMachineVerifierClean() back to false (PR27481)

Put back the isMachineVerifierClean() override removed at rL345513 to fix Windows ThinLTO tests

llvm-svn: 345528

llvm/lib/Target/X86/X86TargetMachine.h

@@ -53,6 +53,10 @@ public:
   TargetLoweringObjectFile *getObjFileLowering() const override {
     return TLOF.get();
   }
+
+  bool isMachineVerifierClean() const override {
+    return false;
+  }
 };
 
 } // end namespace llvm