[clang] Clarify use of contractions in diagnostic messages (PR #116803)

[via cfe-commits]

Sirraide wrote:

I don’t have a very strong opinion on this if the consensus is that this is a change for the better, but as someone with a background in linguistics, I’d argue that this seems like a weird thing to discourage—I don’t think the single quote is really distracting at all if it occurs in a common contraction (e.g. isn’t, aren’t, don’t, doesn’t, etc.), because you simply parse that as one word. Of course, I don’t think we should start writing ‘you’dn’t’ve’ or anything absurd like that, but I don’t think there’s anything wrong w/ normal contractions.

> they can be harder to understand for non-native English speakers.

I also don’t think this is true: simple contractions are one of the first things we teach people, and I’ve yet to meet someone who doesn’t know what e.g. ‘isn’t’ is supposed to mean. Is there any actual precedent for anyone being confused about this?

https://github.com/llvm/llvm-project/pull/116803