Refactor build targets for torch::deploy (#50288)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/50288
torch::deploy will bundle the objects contained in libtorch-python together with frozenpython into a shared library. Therefore, the libtorch-python objs can't bring with them a dependency on system python.
Buck TARGETS are added throughout the caffe2 tree to make available objects or headers that will be needed by torch::deploy but would have brought unsuitable dependencies if accessed using existing targets.
CMakeLists are modified to separate a torch-python-objs object library which lets torch::deploy compile these objs with the same compile flags as libttorch_python used, but without some of the link-time dependencies such as python.
CudaIPCTypes is moved from libtorch_python to libtorch_cuda because it is really not a python binding, and it statically registers a cuda_ipc_callback which would be duplicated if included in each copy of torch::deploy.
Test Plan: no new functionality, just ensure existing tests continue to pass
Reviewed By: malfet
Differential Revision: D25850785
fbshipit-source-id: b0b81c050cbee04e9de96888f8a09d29238a9db8
