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/runtime.h b/src/runtime.h
index 79c0592..c596a17 100644
--- a/src/runtime.h
+++ b/src/runtime.h
@@ -317,7 +317,7 @@
   }
 
   AbstractMethod* GetCalleeSaveMethod(CalleeSaveType type) const {
-    CHECK(HasCalleeSaveMethod(type));
+    DCHECK(HasCalleeSaveMethod(type));
     return callee_save_methods_[type];
   }