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/sched.h

@@ -12,14 +12,7 @@ __BEGIN_DECLS
 #define __need_pid_t
 #include <sys/types.h>
 
-struct sched_param
-{
-	int				sched_priority;			/* Process or thread execution scheduling priority. */
-	int				sched_ss_low_priority;  /* Low scheduling priority for sporadic server. */
-	struct timespec	sched_ss_repl_period;	/* Replenishment period for sporadic server. */
-	struct timespec	sched_ss_init_budget;	/* Initial budget for sporadic server. */
-	int				sched_ss_max_repl;		/* Maximum pending replenishments for sporadic server. */
-};
+#include <bits/types/sched_param.h>
 
 #define SCHED_FIFO		1
 #define SCHED_RR		2