auto merge of #6265 : sanxiyn/rust/xc-packed, r=nikomatsakis

src/test/auxiliary/packed.rs

@@ -0,0 +1,5 @@
+#[packed]
+struct S {
+    a: u8,
+    b: u32
+}

src/test/run-pass/packed-struct-size-xc.rs

@@ -0,0 +1,8 @@
+// xfail-fast
+// aux-build:packed.rs
+
+extern mod packed;
+
+fn main() {
+    assert_eq!(sys::size_of::<packed::S>(), 5);
+}