properly handle fat pointers to uninhabitable types

src/test/ui/debuginfo/debuginfo_with_uninhabitable_field_and_unsized.rs

@@ -0,0 +1,29 @@
+// check-pass
+// compile-flags: -Cdebuginfo=2
+// fixes issue #94149
+
+#![allow(dead_code)]
+
+pub fn main() {
+    let _ = Foo::<dyn FooTrait>::new();
+}
+
+pub struct Foo<T: FooTrait + ?Sized> {
+    base: FooBase,
+    value: T,
+}
+
+impl<T: FooTrait + ?Sized> Foo<T> {
+    pub fn new() -> Box<Foo<T>> {
+        todo!()
+    }
+}
+
+pub trait FooTrait {}
+
+pub struct FooBase {
+    cls: Bar,
+}
+
+// Bar *must* be a fieldless enum
+pub enum Bar {}