[clang] [clang] Avoid warnings about enum mismatch in ternary expressions. NFC. (PR #159338)

[Martin Storsjö via cfe-commits]

mstorsjo wrote:

This is also not very pretty, but again, this is a mostly reasonable warning - unfortunately our diagnostics aren't all in one large enum for (presumably) technical reasons, even if they are forced to be non-overlapping.

https://github.com/llvm/llvm-project/pull/159338