test for duplicate default eii ICE 149985

Co-authored-by: SATVIKsynopsis <futureiitianisme@gmail.com>

Author: jdonszelmann

tests/ui/eii/default/multiple-default-impls.rs

@@ -0,0 +1,8 @@
+#![crate_type = "lib"]
+#![feature(extern_item_impls)]
+
+#[eii(eii1)]
+fn a() {}
+
+#[eii(eii1)]
+fn b() {}