Use a dedicated type instead of a reference for the diagnostic context

This paves the way for tracking more state (e.g. error tainting) in the diagnostic context handle

compiler/rustc_driver_impl/src/lib.rs

@@ -1444,6 +1444,7 @@ fn report_ice(
         fallback_bundle,
     ));
     let dcx = rustc_errors::DiagCtxt::new(emitter);
+    let dcx = dcx.handle();
 
     // a .span_bug or .bug call has already printed what
     // it wants to print.
@@ -1509,7 +1510,7 @@ fn report_ice(
 
     let num_frames = if backtrace { None } else { Some(2) };
 
-    interface::try_print_query_stack(&dcx, num_frames, file);
+    interface::try_print_query_stack(dcx, num_frames, file);
 
     // We don't trust this callback not to panic itself, so run it at the end after we're sure we've
     // printed all the relevant info.