Fix some build warnings in Nacl-specific code

lib/Transforms/NaCl/PromoteIntegers.cpp

 //===- PromoteIntegers.cpp - Promote illegal integers for PNaCl ABI -------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 // A limited set of transformations to promote illegal-sized int types.
 //
 //===----------------------------------------------------------------------===//
@@ skipping 422 matching lines @@
       State.recordConverted(BCInst, NewInst);
     }
   } else if (LoadInst *Load = dyn_cast<LoadInst>(Inst)) {
     if (shouldConvert(Load)) {
       splitLoad(Load, State);
     }
   } else if (StoreInst *Store = dyn_cast<StoreInst>(Inst)) {
     if (shouldConvert(Store->getValueOperand())) {
       splitStore(Store, State);
     }
-  } else if (CallInst *Call = dyn_cast<CallInst>(Inst)) {
+  } else if (isa<CallInst>(Inst)) {
     report_fatal_error("can't convert calls with illegal types");
   } else if (BinaryOperator *Binop = dyn_cast<BinaryOperator>(Inst)) {
     Value *NewInst = NULL;
     if (Binop->getOpcode() == Instruction::AShr) {
       // The AShr operand needs to be sign-extended to the promoted size
       // before shifting. Because the sign-extension is implemented with
       // with AShr, it can be combined with the original operation.
       Value *Op = Binop->getOperand(0);
       Value *ShiftAmount = NULL;
       APInt SignShiftAmt = APInt(
@@ skipping 150 matching lines @@
 
       if (ShouldConvert) {
         convertInstruction(Inst, State);
         Modified = true;
       }
     }
   }
   State.eraseReplacedInstructions();
   return Modified;
 }