Rollup merge of #121669 - nnethercote:count-stashed-errs-again, r=estebank

Count stashed errors again

Stashed diagnostics are such a pain. Their "might be emitted, might not" semantics messes with lots of things.

#120828 and #121206 made some big changes to how they work, improving some things, but still leaving some problems, as seen by the issues caused by #121206. This PR aims to fix all of them by restricting them in a way that eliminates the "might be emitted, might not" semantics while still allowing 98% of their benefit. Details in the individual commit logs.

r? `@oli-obk`

Author: GuillaumeGomez

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.dcx().has_errors().is_some() {
+            if tcx.sess.dcx().has_errors_or_delayed_bugs().is_some() {
                 tcx.dcx().fatal("miri cannot be run on programs that fail compilation");
             }