Hopefully fix UB

Author: Mark-Simulacrum

compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp

@@ -1530,7 +1530,10 @@ extern "C" LLVMValueRef LLVMRustBuildCall(LLVMBuilderRef B, LLVMTypeRef Ty, LLVM
   FunctionType *FTy = unwrap<FunctionType>(Ty);
   return wrap(unwrap(B)->CreateCall(
       FTy, Callee, ArrayRef<Value*>(unwrap(Args), NumArgs),
-      ArrayRef<OperandBundleDef>(*OpBundles, NumOpBundles)));
+      NumOpBundles == 0 ?
+        ArrayRef<OperandBundleDef>() :
+        // FIXME: This signature is just wrong, no idea how this ever worked.
+        ArrayRef<OperandBundleDef>(*OpBundles, NumOpBundles)));
 }
 
 extern "C" LLVMValueRef LLVMRustGetInstrProfIncrementIntrinsic(LLVMModuleRef M) {