Fix a bug that would cause subzero to fail when --threads=0.

src/IceCfgNode.cpp

 //===- subzero/src/IceCfgNode.cpp - Basic block (node) implementation -----===//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // This file implements the CfgNode class, including the complexities
@@ skipping 1238 matching lines @@
 
   GlobalContext *Context = Func->getContext();
 
   bool BadIntrinsic = false;
   const Intrinsics::FullIntrinsicInfo *Info =
       Context->getIntrinsicsInfo().find(RMW_I64, BadIntrinsic);
   assert(!BadIntrinsic);
   assert(Info != nullptr);
 
   Operand *RMWI64Name = Context->getConstantExternSym(RMW_I64);
-  Constant *Counter = Context->getConstantExternSym(Var->getName());
+  constexpr RelocOffsetT Offset = 0;
+  constexpr bool SuppressMangling = true;
+  Constant *Counter =
+      Context->getConstantSym(Offset, Var->getName(), SuppressMangling);
   Constant *AtomicRMWOp = Context->getConstantInt32(Intrinsics::AtomicAdd);
   Constant *One = Context->getConstantInt64(1);
   Constant *OrderAcquireRelease =
       Context->getConstantInt32(Intrinsics::MemoryOrderAcquireRelease);
 
   InstIntrinsicCall *Inst = InstIntrinsicCall::create(
       Func, 5, Func->makeVariable(IceType_i64), RMWI64Name, Info->Info);
   Inst->addArg(AtomicRMWOp);
   Inst->addArg(Counter);
   Inst->addArg(One);
   Inst->addArg(OrderAcquireRelease);
   Insts.push_front(Inst);
 }
 
 } // end of namespace Ice