add test for rust-lang#64784 Declarative macros can create infinite g…

…lob import cycles

Fixes rust-lang#64784

tests/ui/privacy/decl-macro-infinite-global-import-cycle-ice-64784.rs

@@ -0,0 +1,15 @@
+// ICE #64784  already borrowed: BorrowMutError
+//@ check-pass
+#![feature(decl_macro)]
+
+pub macro m($i:ident, $j:ident) {
+    mod $i {
+        pub use crate::$j::*;
+        pub struct A;
+    }
+}
+
+m!(x, y);
+m!(y, x);
+
+fn main() {}