port lgamma from TH to Aten (#25138)
Summary:
https://github.com/pytorch/pytorch/issues/24722
Pull Request resolved: https://github.com/pytorch/pytorch/pull/25138
Differential Revision: D17171782
Pulled By: VitalyFedyunin
fbshipit-source-id: b0026f0ce5306debf19036f97b8624bf0a56f349
