PyTorch -> C++17 (#98209)
This diff locks in C++17 as the minimum standard with which PyTorch can be compiled.
This makes it possible to use all C++17 features in PyTorch.
This breaks backward compatibility in the sense that users with older compilers may find their compilers no longer are sufficient for the job.
Summary: #buildmore
Differential Revision: D44356879
Pull Request resolved: https://github.com/pytorch/pytorch/pull/98209
Approved by: https://github.com/ezyang, https://github.com/malfet, https://github.com/PaliC
