Refactor and remove copy mark bits.

Refactor code GC realted code to be in a GC folder.

Remove copy mark bits by using pointer changing instead.

Enable concurrent sweeping of system weaks.

Fix non concurrent GC plan.

Change-Id: I9c71478be27d21a75f8a4e6af6faabe896e5e263
diff --git a/src/oatdump.cc b/src/oatdump.cc
index 01b2042..e4fc930 100644
--- a/src/oatdump.cc
+++ b/src/oatdump.cc
@@ -33,7 +33,7 @@
 #include "runtime.h"
 #include "safe_map.h"
 #include "scoped_thread_state_change.h"
-#include "space.h"
+#include "gc/space.h"
 #include "stringpiece.h"
 #include "gc_map.h"