Add Directory Check to Prevent Redundant Cloning in Build Process

[vamsivallepu]

What does this PR do?

Fixes #2485

This PR adds a check to the build process that prevents the fbgemm repository from being cloned if the directory already exists, avoiding potential errors when re-running the build.

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
• Did you read the contributor guideline,
  Pull Request section?
• Was this discussed/approved via a Github issue or the forum? Please add a link
  to it if that's the case.
• Did you make sure to update the documentation with your changes? Here are the
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  here are tips on formatting docstrings.
• Did you write any new necessary tests?

Who can review?

Anyone in the community is free to review the PR once the tests have passed.
@OlivierDehaene @Narsil

[ErikKaum]

Hi @vamsivallepu

Thanks for the PR 🙌
I think this should be good to go. Let me first double check 👍

[vamsivallepu]

@ErikKaum Can we merge this?

[ErikKaum]

Ah thanks for reminding me, I've created a branch to run the CI so that it doesn't fail in permissions 👍