fix(FTBFS):adapt to new LLVM 19 DiagnosticHandlerTy
LLVM 19 changed DiagnosticHandlerTy. Both clc and clover need to be updated for this upstream change.
- Reference: https://github.com/llvm/llvm-project/commit/44d037cc258dcf179d2c48c93996bb406ecd0fae
- Closes: #10928 (closed)
- Signed-off-by: Kai Wasserbäch kai@dev.carbon-project.org
- Reviewed-by: Karol Herbst kherbst@redhat.com