[clang] [Clang] Treat the body of an expansion statement with expansion size 0 as discarded (PR #212319)

[Oliver Hunt via cfe-commits]

https://github.com/ojhunt commented:

My only real concern is that `HasExpansionSize` on `CreateEmpty(...)` where I'd really prefer we can construct an "empty" expansion but know we have size I'd really like to avoid the bool condition.

https://github.com/llvm/llvm-project/pull/212319