Fix socket.cpp compilation using gcc-9.4 (#111002)
Otherwise following error is thrown when attempted to compile with WERROR enabled:
```
In file included from /home/nshulga/git/pytorch/pytorch/torch/csrc/distributed/c10d/socket.cpp:30:
/home/nshulga/git/pytorch/pytorch/third_party/fmt/include/fmt/chrono.h:340:24: warning: redundant redeclaration of ‘constexpr’ static data member ‘fmt::v10::detail::codecvt_result<CodeUnit>::max_size’ [-Wdeprecated]
340 | constexpr const size_t codecvt_result<CodeUnit>::max_size;
| ^~~~~~~~~~~~~~~~~~~~~~~~
/home/nshulga/git/pytorch/pytorch/third_party/fmt/include/fmt/chrono.h:335:33: note: previous declaration of ‘fmt::v10::detail::codecvt_result<CodeUnit>::max_size’
335 | static constexpr const size_t max_size = 32;
| ^~~~~~~~
```
or following if using clang as host compiler
```
In file included from /Users/nshulga/git/pytorch/pytorch/torch/csrc/distributed/c10d/socket.cpp:30:
/Users/nshulga/git/pytorch/pytorch/third_party/fmt/include/fmt/chrono.h:340:50: warning: out-of-line definition of constexpr static data member is redundant in C++17 and is deprecated [-Wdeprecated]
constexpr const size_t codecvt_result<CodeUnit>::max_size;
```
Pull Request resolved: https://github.com/pytorch/pytorch/pull/111002
Approved by: https://github.com/drisspg
