LibC: Implement pthread cancelation

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

userspace/libraries/LibC/sys/wait.cpp

@@ -1,13 +1,16 @@
+#include <pthread.h>
 #include <sys/syscall.h>
 #include <sys/wait.h>
 #include <unistd.h>
 
 pid_t wait(int* stat_loc)
 {
+	pthread_testcancel();
 	return waitpid(-1, stat_loc, 0);
 }
 
 pid_t waitpid(pid_t pid, int* stat_loc, int options)
 {
+	pthread_testcancel();
 	return (pid_t)syscall(SYS_WAIT, pid, stat_loc, options);
 }