You're looking at the wrong side of sqlite usage. If you develop sqlite, why wouldn't you test it on every compiler/version combination you can get your hands on? Whether someone uses it in production is irrelevant.
Two things though:
1. Hopefully none of your users run an unreleased clang from head, so you're not using anything a user will run into.
2. Consider if it is it worth the effort to validate every commit pushed to head, or whether you'd get more out of your investment if you only tested releases that received some more vetting (e.g. nightlies).
Yes, but clang eventually gets released. You want to catch bugs in clang and get them fixed before that release happens.
It is not the same as playing with a release candidate.