Add UBSAN build option and fix undefined behaviour errors.

src/IceTargetLoweringX8632Traits.h

Index: src/IceTargetLoweringX8632Traits.h
diff --git a/src/IceTargetLoweringX8632Traits.h b/src/IceTargetLoweringX8632Traits.h
index 3bfd404b76df098334726f24cea339126ded3c7c..9984afba198660fefb9db0cf781590c76e943d68 100644
--- a/src/IceTargetLoweringX8632Traits.h
+++ b/src/IceTargetLoweringX8632Traits.h
@@ -550,7 +550,7 @@ template <> struct MachineTraits<TargetX8632> {
     X86Operand &operator=(const X86Operand &) = delete;
 
   public:
-    enum OperandKindX8632 { k__Start = ::Ice::Operand::kTarget, kMem, kSplit };
+    enum OperandKindX8632 { k__Start = ::Ice::Operand::kTarget0, kMem, kSplit };
     using ::Ice::Operand::dump;
 
     void dump(const Cfg *, Ostream &Str) const override;
@@ -675,7 +675,7 @@ template <> struct MachineTraits<TargetX8632> {
       return new (Func->allocate<SpillVariable>()) SpillVariable(Ty, Index);
     }
     const static OperandKind SpillVariableKind =
-        static_cast<OperandKind>(kVariable_Target);
+        static_cast<OperandKind>(kVariable_Target0);
     static bool classof(const Operand *Operand) {
       return Operand->getKind() == SpillVariableKind;
     }