rewrite and rename issue-53964

Author: Oneirical

src/tools/tidy/src/allowed_run_make_makefiles.txt

@@ -116,7 +116,6 @@ run-make/issue-46239/Makefile
 run-make/issue-47384/Makefile
 run-make/issue-47551/Makefile
 run-make/issue-51671/Makefile
-run-make/issue-53964/Makefile
 run-make/issue-64153/Makefile
 run-make/issue-68794-textrel-on-minimal-lib/Makefile
 run-make/issue-69368/Makefile

tests/run-make/issue-53964/app.rs renamed to tests/run-make/external-crate-panic-handle-no-lint/app.rs

@@ -0,0 +1,12 @@
+// Defining a crate that provides panic handling as an external crate
+// could uselessly trigger the "unused external crate" lint. In this test,
+// if the lint is triggered, it will trip #![deny(unused_extern_crates)],
+// and cause the test to fail.
+// See https://github.com/rust-lang/rust/issues/53964
+
+use run_make_support::{rustc, tmp_dir};
+
+fn main() {
+    rustc().input("panic.rs").run();
+    rustc().input("app.rs").panic("abort").emit("obj").library_search_path(tmp_dir()).run();
+}