Add alignment attribute to packed.

Make packed objects 4 byte aligned or else GCC becomes paranoid and
assumes only byte alignment on whole objects.
Change CHECK in GetCalleeSaveMethod to DCHECK to encourage inlining.

Change-Id: I79f1a13752492413c919b36f4e207e637647834f
diff --git a/src/stack.h b/src/stack.h
index 1dfd5b6..1134b25 100644
--- a/src/stack.h
+++ b/src/stack.h
@@ -236,7 +236,7 @@
 // may either be shadow frames or lists of frames using fixed frame sizes. Transition records are
 // necessary for transitions between code using different frame layouts and transitions into native
 // code.
-class PACKED ManagedStack {
+class PACKED(4) ManagedStack {
  public:
   ManagedStack()
       : link_(NULL), top_shadow_frame_(NULL), top_quick_frame_(NULL), top_quick_frame_pc_(0) {}