LibC: Cleanup pthread code and add some pthread_attr functions

errno, pthread cleanup and pthread id are now stored in uthread. This
allows using these without TLS

userspace/libraries/LibC/include/mqueue.h

@@ -10,11 +10,12 @@ __BEGIN_DECLS
 #include <time.h>
 #include <signal.h>
 
-#define __need_pthread_attr_t
 #define __need_size_t
 #define __need_ssize_t
 #include <sys/types.h>
 
+#include <bits/types/pthread_attr_t.h>
+
 typedef int mqd_t;
 
 struct mq_attr