[CodeGen] Fix unused variable warning (NFC)

Author: nikic

clang/lib/CodeGen/CodeGenModule.cpp

@@ -2935,7 +2935,7 @@ void CodeGenModule::SetFunctionAttributes(GlobalDecl GD, llvm::Function *F,
                                           bool IsIncompleteFunction,
                                           bool IsThunk) {
 
-  if (llvm::Intrinsic::ID IID = F->getIntrinsicID()) {
+  if (F->getIntrinsicID() != llvm::Intrinsic::not_intrinsic) {
     // If this is an intrinsic function, the attributes will have been set
     // when the function was created.
     return;