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/oat.h b/src/oat.h
index 96ed4c4..254be1a 100644
--- a/src/oat.h
+++ b/src/oat.h
@@ -25,7 +25,7 @@
 
 namespace art {
 
-class PACKED OatHeader {
+class PACKED(4) OatHeader {
  public:
   OatHeader();
   OatHeader(InstructionSet instruction_set,
@@ -68,7 +68,7 @@
   DISALLOW_COPY_AND_ASSIGN(OatHeader);
 };
 
-class PACKED OatMethodOffsets {
+class PACKED(4) OatMethodOffsets {
  public:
   OatMethodOffsets();