Rollup merge of #121206 - nnethercote:top-level-error-handling, r=oli-obk

Top level error handling

The interactions between the following things are surprisingly complicated:
- `emit_stashed_diagnostics`,
- `flush_delayed`,
- normal return vs `abort_if_errors`/`FatalError.raise()` unwinding in the call to the closure in `interface::run_compiler`.

This PR disentangles it all.

r? `@oli-obk`

Author: matthiaskrgr

src/bin/miri.rs

@@ -68,7 +68,7 @@ impl rustc_driver::Callbacks for MiriCompilerCalls {
         queries: &'tcx rustc_interface::Queries<'tcx>,
     ) -> Compilation {
         queries.global_ctxt().unwrap().enter(|tcx| {
-            if tcx.sess.compile_status().is_err() {
+            if tcx.sess.dcx().has_errors().is_some() {
                 tcx.dcx().fatal("miri cannot be run on programs that fail compilation");
             }