Update FP16 to latest master (#14498)
Summary:
TSIA - fp16 cmake had a bug that is fixed in https://github.com/Maratyszcza/FP16/pull/9 .
Pull Request resolved: https://github.com/pytorch/pytorch/pull/14498
Differential Revision: D13240829
Pulled By: Yangqing
fbshipit-source-id: 724745750efe4f1b49d29ee07380c36997579915
