CMake/Ninja: fix dependencies for .cu files (#36938)
Summary:
Fixes https://github.com/pytorch/pytorch/issues/26304
After this patch `build.ninja` entries for `.cu` files will contain a `depfile` variable pointing to a `.NVCC-depend` file containing dependencies (i.e., header files included directly or indirectly) of the `.cu` source file. Until now, those `.NVCC-depend` files were being transposed into `.cu.o.depend` files in CMake format. That did not work as intended because the `.cu.o` target file was declared to be dependent on the `.cu.o.depend` file itself, rather than its contents. In fact, Ninja lacks the functionality to process dependencies in the CMake format of those `.cu.o.depend` files.
This was tested on Linux as described in https://github.com/pytorch/pytorch/issues/26304#issuecomment-614667170
I have also verified that the original problem does not reproduce with Makefiles (i.e., when `ninja` is not present in the system) and that PyTorch still build successfully with Makefiles after this patch.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/36938
Differential Revision: D21156042
Pulled By: ezyang
fbshipit-source-id: fda3aaa57207f4d6bf74d2f254fe45fb7fd90eec
