Fix derivative of sinc at x=0 (#56763)
Summary:
Attempting to fix https://github.com/pytorch/pytorch/issues/56760
The derivative of `sinc(x)` at `x=0` should be special cased to 0.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/56763
Reviewed By: zhangguanheng66
Differential Revision: D27978135
Pulled By: albanD
fbshipit-source-id: ede5e734613cf60e720f6bcc7387c3cd9c6ec233
