fix(build): special case inconsistently-cased paths in LLVM build

[shahms]

Fixes #4535

[googlebot]

We found a Contributor License Agreement for you (the sender of this pull request), but were unable to find agreements for all the commit author(s) or Co-authors. If you authored these, maybe you used a different email address in the git commits than was used to sign the CLA (login here to double check)? If these were authored by someone else, then they will need to sign a CLA as well, and confirm that they're okay with these being contributed to Google.
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[shahms]

Ugh, I knew I shouldn't have done that.

@johnedmonds any chance you can go to https://cla.developers.google.com/ and sign the Google CLA? Our compliance bot is picky and because I applied the changes from the web UI rather than manually it's going to attribute them to you. If you don't want to sign the CLA I can (probably?) revert the auto-commits and make the fixes myself.

[johnedmonds]

Sorry about that. Any chance you could change the author to jedmonds@spotify.com which has signed the CLA? (I just changed the default address on my profile page if that helps.) Otherwise, you can just revert and re-apply the changes yourself.

[shahms]

I don't believe I can (or at least, have no idea how I would), but I believe you should be able to add the @gmail.com address at the linked page?

[johnedmonds]

Done. Signed the CLA 👍 .

[googlebot]

CLAs look good, thanks!

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