Vectorize unary operator erfinv (#26629)
Summary:
Resolves https://github.com/pytorch/pytorch/issues/19088 for erfinv.
erfinv speedup (MKL, AMD Ryzen Threadripper 2970WX 24-Core Processor): 22x
Pull Request resolved: https://github.com/pytorch/pytorch/pull/26629
Differential Revision: D17527230
Pulled By: ezyang
fbshipit-source-id: 0a5a53a88f7eb219617120383a454a01ad78279a
