LibC: Implement pthread cancelation

This code is not tested at all but it looks correct xD

userspace/libraries/LibC/include/pthread.h

@@ -32,10 +32,13 @@ struct uthread
 	struct _pthread_cleanup_t* cleanup_stack;
 	pthread_t id;
 	int errno_;
+	int cancel_type;
+	int cancel_state;
+	int canceled;
 	uintptr_t dtv[];
 };
 
-#define PTHREAD_CANCELED				1
+#define PTHREAD_CANCELED				(void*)1
 
 #define PTHREAD_CANCEL_ASYNCHRONOUS		1
 #define PTHREAD_CANCEL_DEFERRED			0
@@ -43,6 +46,9 @@ struct uthread
 #define PTHREAD_CANCEL_DISABLE			0
 #define PTHREAD_CANCEL_ENABLE			1
 
+// cancellation points
+// https://pubs.opengroup.org/onlinepubs/9799919799/functions/V2_chap02.html#tag_16_09_05_02
+
 #define PTHREAD_PRIO_INHERIT			1
 #define PTHREAD_PRIO_NONE				0
 #define PTHREAD_PRIO_PROTECT			2

userspace/libraries/LibC/include/signal.h

@@ -106,7 +106,8 @@ struct sigevent
 #define SIGXCPU   27
 #define SIGXFSZ   28
 #define SIGWINCH  29
-#define SIGRTMIN  30
+#define SIGCANCEL 30
+#define SIGRTMIN  31
 #define SIGRTMAX  (SIGRTMIN+32)
 
 #define NSIG SIGRTMAX