tests: Reproduce the issue with missing MIR for ambiguous reexports

tests/ui/imports/ambiguous-reachable.rs

@@ -0,0 +1,10 @@
+//@ build-fail
+//@ aux-crate: ambiguous_reachable_extern=ambiguous-reachable-extern.rs
+
+#![allow(ambiguous_glob_imports)]
+
+fn main() {
+    ambiguous_reachable_extern::generic::<u8>();
+}
+
+//~? ERROR missing optimized MIR

tests/ui/imports/ambiguous-reachable.stderr

@@ -0,0 +1,31 @@
+error: missing optimized MIR for `ambiguous_reachable_extern::m1::generic::<u8>` in the crate `ambiguous_reachable_extern`
+   |
+note: missing optimized MIR for this item (was the crate `ambiguous_reachable_extern` compiled with `--emit=metadata`?)
+  --> $DIR/auxiliary/ambiguous-reachable-extern.rs:2:5
+   |
+LL |     pub fn generic<T>() {
+   |     ^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 1 previous error
+
+Future incompatibility report: Future breakage diagnostic:
+warning: `generic` is ambiguous
+  --> $DIR/ambiguous-reachable.rs:7:33
+   |
+LL |     ambiguous_reachable_extern::generic::<u8>();
+   |                                 ^^^^^^^ ambiguous name
+   |
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #114095 <https://github.com/rust-lang/rust/issues/114095>
+   = note: ambiguous because of multiple glob imports of a name in the same module
+note: `generic` could refer to the function defined here
+  --> $DIR/auxiliary/ambiguous-reachable-extern.rs:13:9
+   |
+LL | pub use m1::*;
+   |         ^^
+note: `generic` could also refer to the function defined here
+  --> $DIR/auxiliary/ambiguous-reachable-extern.rs:14:9
+   |
+LL | pub use m2::*;
+   |         ^^
+

tests/ui/imports/auxiliary/ambiguous-reachable-extern.rs

@@ -0,0 +1,14 @@
+mod m1 {
+    pub fn generic<T>() {
+        let x = 10;
+        let y = 11;
+        println!("hello {x} world {:?}", y);
+    }
+}
+
+mod m2 {
+    pub fn generic() {}
+}
+
+pub use m1::*;
+pub use m2::*;