Check that we do not ICE when anonymous lifetimes appear in AnonConst.

Fixes #98932.

src/test/ui/impl-header-lifetime-elision/constant-used-as-arraylen.rs

@@ -0,0 +1,24 @@
+// check-pass
+// Verify that we do not ICE when anonymous lifetimes appear inside an AnonConst.
+
+pub struct EntriesBuffer(Box<[[u8; HashesEntry::LEN]; 5]>);
+
+impl EntriesBuffer {
+    pub fn iter_child_buffers(&mut self) -> impl Iterator<Item = &mut [u8; HashesEntry::LEN]> {
+        self.0.iter_mut()
+    }
+
+    pub fn iter_child_buffers_explicit(
+        &mut self,
+    ) -> impl Iterator<Item = &mut [u8; HashesEntry::<'_>::LEN]> {
+        self.0.iter_mut()
+    }
+}
+
+pub struct HashesEntry<'a>(&'a [u8]);
+
+impl HashesEntry<'_> {
+    pub const LEN: usize = 1;
+}
+
+fn main() {}