[Reland2] fix missing-prototypes warnings in torch_cpu (Part 4) (#102228)
This PR relands the changes introduced in PR https://github.com/pytorch/pytorch/pull/100849. The old PR turnd nnc_* functions into static. We now add declarations for them and hope that inter builds will pass.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/102228
Approved by: https://github.com/albanD
