Fix intermittent link errors in NCCL build (#84245)
Should fix #13362 and fix #83790
I think I've discovered the root cause of the intermittent nccl link
failures. If we look at the variable name in the redefinition error:
```
_02021d91_11_sendrecv_cu_0bc7b9c8_11152
```
this is the name of the file being compiled + some form of unique ID.
As part of NCCL's build process, the same file is compiled multiple
times with different macro definitions depending on which operator and
dtype are being compiled, e.g.
```
nvcc -DNCCL_OP=0 -DNCCL_TYPE=0 -dc sendrecv.cu -o sendrecv_sum_i8.o
```
Since the filename parts are the same, then if the unique IDs also
happen to collide then the entire identifier will collide and the link
fails. So the fix here is to generate a unique `.cu` file for each
object file. I've implemented this as a `.patch` file that gets
applied from our cmake code, but if we instead fork nccl that would be
cleaner.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/84245
Approved by: https://github.com/janeyx99, https://github.com/malfet
