Fix build failure on OSX (#23998)
Summary:
https://github.com/pytorch/pytorch/pull/23228 caused build failure on OSX, because rpc.h is included as long as USE_DISTRIBUTED=1, but rpc/init.cpp (and others) is only included when NOT APPLE. So, it cannot find python_functions defined in init.cpp on MacOS. This PR attempt to fix it by wrapping rpc.h with USE_C10D, which is only set when NOT APPLE.
I tried this fix locally and it works.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/23998
Differential Revision: D16706087
Pulled By: mrshenli
fbshipit-source-id: d04fe6717a181a3198289cdef51439708c2e291d
