message: Add an assertion on the builder to ensure that a block is set before creating an operation
  This is more friendly for the user than a raw segfault
diff: @@ -310,6 +310,7 @@ Block *FuncBuilder::createBlock(Block *insertBefore) {
  /// Create an operation given the fields represented as an OperationState.
  Instruction *FuncBuilder::createOperation(const OperationState &state) {
  + assert(block && "createOperation() called without setting builder's block");
  auto *op = Instruction::create(state.location, state.name, state.operands,
  state.types, state.attributes,
  state.successors, state.numBlockLists,
  