Fix LLVM-12 concat_split_op.h error (#66060)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/66060
Fixes
```
testTumHistoryAdditionalLaser (caffe2.caffe2.fb.layers.tests.tum_history_test.TestTumHistory) ... caffe2/caffe2/operators/concat_split_op.h:363:74: runtime error: applying non-zero offset 8 to null pointer
#0 0x7f8f39d29795 in caffe2::ConcatOp<caffe2::CPUContext>::RunOnDevice() caffe2/caffe2/operators/concat_split_op.h:363
#1 0x7f8f39c4978d in caffe2::Operator<caffe2::CPUContext>::Run(int) caffe2/caffe2/core/operator.h:987
#2 0x7f8f381fe9c9 in caffe2::SimpleNet::Run() caffe2/caffe2/core/net_simple.cc:67
#3 0x7f8f38ee488e in caffe2::Workspace::RunNet(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&) caffe2/caffe2/core/workspace.cc:289
```
Test Plan: Sandcastle
Reviewed By: dzhulgakov, xush6528
Differential Revision: D31366205
fbshipit-source-id: 566aa519677c9d371189e4b1f81d595732861efc
