feat(llvm.sh): long options support

[tcely]

I added support for --help with a change to give a successful exit code.

TODO:

• Split out changes unrelated to --help into other pull requests
• Other things that I forgot to list here

Fixes #33

[sylvestre]

Thanks

I would prefer different pr per classes of changes.
You are mixing different things in the same pr

[tcely]

Thanks

I would prefer different pr per classes of changes. You are mixing different things in the same pr

No problem. I've added splitting up these changes to the list.

This pull request now only has the long options changes.

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