Change order of thread-context members

Because 'stack' and 'stack_base' are related to each other, it makes
sense to locate both members close to each other.

base/include/base/thread.h

@@ -99,11 +99,6 @@ namespace Genode {
 				 */
 				long stack[];
 
-				/**
-				 * Pointer to corresponding 'Thread_base' object
-				 */
-				Thread_base *thread_base;
-
 				/**
 				 * Virtual address of the start of the stack
 				 *
@@ -113,6 +108,11 @@ namespace Genode {
 				 */
 				addr_t stack_base;
 
+				/**
+				 * Pointer to corresponding 'Thread_base' object
+				 */
+				Thread_base *thread_base;
+
 				/**
 				 * Dataspace containing the backing store for the thread context
 				 *