Make Transformers compilable by C++17 (#90389)
`register` keyword is removed in C++17, but keeping it there under ifdef
as I have not measured the perf implication on older compiler, though
there shouldn't be any: all modern compilers supposed to downright
ignore it.
This code originates from https://github.com/facebookresearch/xformers/pull/375 will propose similar PR to remove register keyword usage to that repo.
Yet another thing discovered while working on https://github.com/pytorch/pytorch/pull/85969
Pull Request resolved: https://github.com/pytorch/pytorch/pull/90389
Approved by: https://github.com/drisspg
