support complex types for tanh_backward_cpu (#37791)
Summary:
Closes: https://github.com/pytorch/pytorch/issues/37701
TO-DO:
* [x] Add Tests
Pull Request resolved: https://github.com/pytorch/pytorch/pull/37791
Differential Revision: D21619827
Pulled By: anjali411
fbshipit-source-id: 0919ec80168a7f8b8092da8d39b8bc6f519d3440
