[clang] [webkit.RefCntblBaseVirtualDtor] Make ThreadSafeRefCounted not generate warnings (PR #107676)

[Ryosuke Niwa via cfe-commits]

rniwa wrote:

> > Looks like you're putting no restrictions on what the opaque function is. This may cause some false negatives but it's probably ultimately ok, but it might be a good idea to confirm.
> 
> Yes, we're not putting any requirement for the functions for now.

Actually, why not. We can just require the function names to be ensureOnMainThread or ensureOnMainRunLoop for now. We can relax the requirement further if we find more cases.

https://github.com/llvm/llvm-project/pull/107676