LibC: Implement dummy pthread_attr_{get,set}detachstate

detached threads are not yet supported, but this allows implementation
to make sure threads are joinable.

userspace/libraries/LibC/include/pthread.h

@@ -29,8 +29,6 @@ struct uthread
 #define PTHREAD_CANCEL_DEFERRED			4
 #define PTHREAD_CANCEL_DISABLE			5
 #define PTHREAD_CANCELED				6
-#define PTHREAD_CREATE_DETACHED			7
-#define PTHREAD_CREATE_JOINABLE			8
 #define PTHREAD_EXPLICIT_SCHED			9
 #define PTHREAD_INHERIT_SCHED			10
 #define PTHREAD_PRIO_INHERIT			18
@@ -39,6 +37,9 @@ struct uthread
 #define PTHREAD_SCOPE_PROCESS			23
 #define PTHREAD_SCOPE_SYSTEM			24
 
+#define PTHREAD_CREATE_DETACHED			1
+#define PTHREAD_CREATE_JOINABLE			0
+
 #define PTHREAD_BARRIER_SERIAL_THREAD	1
 
 #define PTHREAD_ONCE_INIT				0