Cache common constants before lowering.

src/IceTargetLoweringX8664.h

Index: src/IceTargetLoweringX8664.h
diff --git a/src/IceTargetLoweringX8664.h b/src/IceTargetLoweringX8664.h
index bd688e534554c5b0ddeca655f84121106dc11449..69500f0efd0d4a01d6bc2b0848c6a46a1372a8be 100644
--- a/src/IceTargetLoweringX8664.h
+++ b/src/IceTargetLoweringX8664.h
@@ -74,7 +74,7 @@ private:
 
   Operand *createNaClReadTPSrcOperand() {
     Variable *TDB = makeReg(IceType_i32);
-    InstCall *Call = makeHelperCall(H_call_read_tp, TDB, 0);
+    InstCall *Call = makeHelperCall(RuntimeHelper::H_call_read_tp, TDB, 0);
     lowerCall(Call);
     return TDB;
   }