Fix string_view::equals_ compilation by CUDA-11.3 (#57322)
Summary:
__builtin_memcmp is not a constexpr for character arrays for NVCC-11.3 compiler.
Attempts to compile this code results in the following error:
```
/opt/conda/lib/python3.6/site-packages/torch/include/c10/util/string_view.h(585): note: constexpr memory comparison is only supported for top-level integer or array-of-integer objects
/opt/conda/lib/python3.6/site-packages/torch/include/c10/util/string_view.h(340): note: called from:
/opt/conda/lib/python3.6/site-packages/torch/include/c10/util/string_view.h(369): note: called from:
```
Fixes #{issue number}
Pull Request resolved: https://github.com/pytorch/pytorch/pull/57322
Reviewed By: janeyx99
Differential Revision: D28119125
Pulled By: malfet
fbshipit-source-id: e5ff6ac7bb42022e86c9974919e055cf82c2ea83
