rewrite extern-fn-with-packed-struct to rmake

Author: Oneirical

Diff for: src/tools/tidy/src/allowed_run_make_makefiles.txt

@@ -30,7 +30,6 @@ run-make/extern-flag-disambiguates/Makefile
 run-make/extern-fn-generic/Makefile
 run-make/extern-fn-mangle/Makefile
 run-make/extern-fn-reachable/Makefile
-run-make/extern-fn-with-packed-struct/Makefile
 run-make/extern-fn-with-union/Makefile
 run-make/extern-multiple-copies/Makefile
 run-make/extern-multiple-copies2/Makefile

Diff for: tests/run-make/extern-fn-with-packed-struct/Makefile

@@ -0,0 +1,17 @@
+// Packed structs, in C, occupy less bytes in memory, but are more
+// vulnerable to alignment errors. Passing them around in a Rust-C foreign
+// function interface (FFI) would cause unexpected behavior, until this was
+// fixed in #16584. This test checks that a Rust program with a C library
+// compiles and executes successfully, even with usage of a packed struct.
+// See https://github.com/rust-lang/rust/issues/16574
+
+//@ ignore-cross-compile
+// Reason: the compiled binary is executed
+
+use run_make_support::{build_native_static_lib, run, rustc};
+
+fn main() {
+    build_native_static_lib("test");
+    rustc().input("test.rs").run();
+    run("test");
+}