Make find_first_set works on x86 MSVC (#38637)
Summary:
Fixes https://github.com/pytorch/pytorch/issues/38322#issuecomment-630031072.
Tested locally.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/38637
Differential Revision: D21620059
Pulled By: ezyang
fbshipit-source-id: 50af50ce29e46759f11a196fa0fedca2740214bb
