Add test for passing/getting packed structs with ffi.

src/test/run-make/extern-fn-with-packed-struct/Makefile

@@ -0,0 +1,7 @@
+-include ../tools.mk
+
+all:
+	$(CC) -std=c99 test.c -c -o $(TMPDIR)/test.o
+	$(AR) rcs $(TMPDIR)/libtest.a $(TMPDIR)/test.o
+	$(RUSTC) test.rs -L $(TMPDIR)
+	$(call RUN,test) || exit 1

src/test/run-make/extern-fn-with-packed-struct/test.c

@@ -0,0 +1,9 @@
+struct __attribute__((packed)) Foo {
+    char a;
+    short b;
+    char c;
+};
+
+struct Foo foo(struct Foo foo) {
+    return foo;
+}

src/test/run-make/extern-fn-with-packed-struct/test.rs

@@ -0,0 +1,30 @@
+// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#[packed]
+#[deriving(PartialEq, Show)]
+struct Foo {
+    a: i8,
+    b: i16,
+    c: i8
+}
+
+#[link(name = "test", kind = "static")]
+extern {
+    fn foo(f: Foo) -> Foo;
+}
+
+fn main() {
+    unsafe {
+        let a = Foo { a: 1, b: 2, c: 3 };
+        let b = foo(a);
+        assert_eq!(a, b);
+    }
+}