Rollup merge of #111573 - compiler-errors:erase-re-error, r=WaffleLapkin

Erase `ReError` properly

Fixes #111341

Since we check whether a type has free regions before erasing (to short circuit unnecesary folding), we need to consider `ReError` as a free region, or else we'll skip it when erasing a type that only mentions `ReError`.

cc `@nnethercote`

compiler/rustc_middle/src/ty/sty.rs

@@ -1708,7 +1708,9 @@ impl<'tcx> Region<'tcx> {
             ty::ReErased => {
                 flags = flags | TypeFlags::HAS_RE_ERASED;
             }
-            ty::ReError(_) => {}
+            ty::ReError(_) => {
+                flags = flags | TypeFlags::HAS_FREE_REGIONS;
+            }
         }
 
         debug!("type_flags({:?}) = {:?}", self, flags);