[llvm] [Support] Fix buffer overflow in regcomp (PR #76681)

[Nikita Popov via llvm-commits]

nikic wrote:

What's the regex that causes this issue? I'm not sure this fix is correct -- I don't think we should be emitting an `OCH_` that skips over `OEND` in the first place.

https://github.com/llvm/llvm-project/pull/76681