[llvm] [llvm][cmake] Error if lldb project is enabled without clang (PR #149055)

[Pavel Labath via llvm-commits]

labath wrote:

> We could do what flang does and enable clang automatically, but I personally prefer making the user make the choice.

I would prefer that too, but I think there's also value in consistency. Unless you're really set on this, I think we should do what flang does.

https://github.com/llvm/llvm-project/pull/149055