Switch internal CUDA build to C++14 (#26757)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/26757
This doesn't switch any open source builds or CI.
The internal fbcode build is C++17 already for quite some time, but in CUDA code, we had it restricted to C++11.
This diff changes that to C++14.
Because this doesn't change anything open source, the risk of this is low.
ghstack-source-id: 90728524
Test Plan: waitforsandcastle
Differential Revision: D17558142
fbshipit-source-id: 9cfd47e38e71d5a2fdae2f535c01f281bf007d9a
