Add test from rust-lang#124901.

Issue rust-lang#124901 was an OOM caused by a query cycle. It was fixed by
a complex change in PR rust-lang#138672, but that PR did not add the test case.
Let's add it now, because it's the only known reproducer of the OOM.

Author: nnethercote

tests/ui/resolve/query-cycle-issue-124901.rs

@@ -0,0 +1,24 @@
+//~ ERROR: cycle detected when looking up span for `Default`
+trait Default {
+    type Id;
+
+    fn intu(&self) -> &Self::Id;
+}
+
+impl<T: Default<Id = U>, U: Copy> Default for U {
+    default type Id = T;
+    fn intu(&self) -> &Self::Id {
+        self
+    }
+}
+
+fn specialization<T>(t: T) -> U {
+    *t.intu()
+}
+
+use std::num::NonZero;
+
+fn main() {
+    let assert_eq = NonZero::<u8, Option<NonZero<u8>>>(0);
+    assert_eq!(specialization, None);
+}

tests/ui/resolve/query-cycle-issue-124901.stderr

@@ -0,0 +1,9 @@
+error[E0391]: cycle detected when looking up span for `Default`
+   |
+   = note: ...which immediately requires looking up span for `Default` again
+   = note: cycle used when perform lints prior to AST lowering
+   = note: see https://rustc-dev-guide.rust-lang.org/overview.html#queries and https://rustc-dev-guide.rust-lang.org/query.html for more information
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0391`.