Improve no-CUDA detecton, add gloo
Author: Yard1
Pull request: yes

# What does this PR do?

Previously, if `no_cuda` was set to False and `local_rank!=-1`, `TrainingArguments._setup_devices` would still try to use a `cuda` device despite it being non-available, causing an exception. This PR fixes this issue, and adds `gloo` to allowed `xpi_backend`s.

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Comments:
cc @sgugger 

_The documentation is not available anymore as the PR was closed or merged._

I am unsure what you are trying to fix, as it is the intended behavior. The user has to explicitly opt-in to DDP on CPU with the flag `--no_cuda` and should receive an error otherwise if the GPUs are not visible for some reason.

Hmm, I see. From the description of the `no_cuda` argument, I inferred that the default behavior is to use CUDA if available, and fall back to CPU otherwise. This behavior is also seen with the `DataParallel` case. If it is intended that the user has to set this explicitly, then feel free to close the PR.