USE_TORCH while import transformers forever true
## Environment info
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- `transformers` version: 4.8.0
- Platform: linux
- Python version: 3.6
- PyTorch version (GPU?):1.8.1(No)
- Tensorflow version (GPU?):2.0.1(No)
- Using GPU in script?:No
- Using distributed or parallel set-up in script?:No

### Who can help
@sgugger @Rocketknight1 
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Models:

- albert, bert, xlm: @LysandreJik
- blenderbot, bart, marian, pegasus, encoderdecoder,  t5: @patrickvonplaten, @patil-suraj
- longformer, reformer, transfoxl, xlnet: @patrickvonplaten
- fsmt: @stas00
- funnel: @sgugger
- gpt2: @patrickvonplaten, @LysandreJik
- rag: @patrickvonplaten, @lhoestq
- tensorflow: @Rocketknight1

Library:

- benchmarks: @patrickvonplaten
- deepspeed: @stas00
- ray/raytune: @richardliaw, @amogkam
- text generation: @patrickvonplaten
- tokenizers: @LysandreJik
- trainer: @sgugger
- pipelines: @LysandreJik

Documentation: @sgugger


 -->

## Information

Model I am using (Bert, XLNet ...):AutoTokenizer(Bert)

The problem arises when using:
* Importing transformers while Using TensorFlow backend
error arises : 
```transformers/file_utils.py``` 
```if _torch_available:
    280     torch_version = version.parse(importlib_metadata.version("torch"))
--> 281     _torch_fx_available = (torch_version.major, torch_version.minor) == (
    282         TORCH_FX_REQUIRED_VERSION.major,
    283         TORCH_FX_REQUIRED_VERSION.minor,

AttributeError: 'Version' object has no attribute 'major'
```


The tasks I am working on is:
* [ ] trying to use ```train_new_from_iterator``` on top of ```bert-base-cased``` 
* [ ] my own task or dataset: (give details below)

## To reproduce

Steps to reproduce the behavior:

1. https://github.com/huggingface/transformers/pull/9441
2. row 67, forever True (```USE_TORCH```) So cannot reach (```USE_TF```) , row 80

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## Expected behavior
allow transformers import, when using TF

<!-- A clear and concise description of what you would expect to happen. -->

I am unsure of what the bug is and the reproducer you are suggesting. You are not supposed to change the source code of the library to activate `USE_TORCH`, you should set it as an environment variable.<|||||>Please close issue,
Something wrong with my env

בתאריך יום ב׳, 12 ביולי 2021 ב-17:33 מאת Sylvain Gugger <
***@***.***>:

> I am unsure of what the bug is and the reproducer you are suggesting. You
> are not supposed to change the source code of the library to activate
> USE_TORCH, you should set it as an environment variable.
>
> —
> You are receiving this because you authored the thread.
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> <https://github.com/huggingface/transformers/issues/12641#issuecomment-878330631>,
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