Make HandleCycleError an enum instead of a macro-generated closure

- Add a `HandleCycleError` enum to rustc_query_system, along with a `handle_cycle_error` function
- Move `Value` to rustc_query_system, so `handle_cycle_error` can use it
- Move the `Value` impls from rustc_query_impl to rustc_middle. This is necessary due to orphan rules.

compiler/rustc_middle/src/lib.rs

@@ -95,6 +95,7 @@ pub mod mir;
 pub mod thir;
 pub mod traits;
 pub mod ty;
+mod values;
 
 pub mod util {
     pub mod bug;