Track undefined sym in the symtab. Remove hack for missing relocs against undef.

src/IceTargetLoweringX8632.h

 //===- subzero/src/IceTargetLoweringX8632.h - x86-32 lowering ---*- C++ -*-===//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // This file declares the TargetLoweringX8632 class, which
@@ skipping 135 matching lines @@
   typedef uint32_t LegalMask;
   Operand *legalize(Operand *From, LegalMask Allowed = Legal_All,
                     int32_t RegNum = Variable::NoRegister);
   Variable *legalizeToVar(Operand *From, int32_t RegNum = Variable::NoRegister);
   // Turn a pointer operand into a memory operand that can be
   // used by a real load/store operation. Legalizes the operand as well.
   // This is a nop if the operand is already a legal memory operand.
   OperandX8632Mem *FormMemoryOperand(Operand *Ptr, Type Ty);
 
   Variable *makeReg(Type Ty, int32_t RegNum = Variable::NoRegister);
+  // Make a call to an external helper function.
   InstCall *makeHelperCall(const IceString &Name, Variable *Dest,
                            SizeT MaxSrcs) {
-    const bool SuppressMangling = true;
     const bool HasTailCall = false;
-    const RelocOffsetT Offset = 0;
-    Constant *CallTarget = Ctx->getConstantSym(Offset, Name, SuppressMangling);
+    Constant *CallTarget = Ctx->getConstantExternSym(Name);
     InstCall *Call =
         InstCall::create(Func, MaxSrcs, Dest, CallTarget, HasTailCall);
     return Call;
   }
   static Type stackSlotType();
 
   Variable *copyToReg(Operand *Src, int32_t RegNum = Variable::NoRegister);
 
   // Returns a vector in a register with the given constant entries.
   Variable *makeVectorOfZeros(Type Ty, int32_t RegNum = Variable::NoRegister);
@@ skipping 339 matching lines @@
 };
 
 template <> void ConstantInteger32::emit(GlobalContext *Ctx) const;
 template <> void ConstantInteger64::emit(GlobalContext *Ctx) const;
 template <> void ConstantFloat::emit(GlobalContext *Ctx) const;
 template <> void ConstantDouble::emit(GlobalContext *Ctx) const;
 
 } // end of namespace Ice
 
 #endif // SUBZERO_SRC_ICETARGETLOWERINGX8632_H