Kernel/LibC: Implement all chown family function with fchownat

userspace/libraries/LibC/include/sys/syscall.h

@@ -57,7 +57,7 @@ __BEGIN_DECLS
 	O(SYS_READLINKAT,		readlinkat)		\
 	O(SYS_MSYNC,			msync)			\
 	O(SYS_PREAD,			pread)			\
-	O(SYS_CHOWN,			chown)			\
+	O(SYS_FCHOWNAT,			fchownat)		\
 	O(SYS_LOAD_KEYMAP,		load_keymap)	\
 	O(SYS_SOCKET,			socket)			\
 	O(SYS_BIND,				bind)			\

userspace/libraries/LibC/unistd.cpp

@@ -315,7 +315,22 @@ int chdir(const char* path)
 
 int chown(const char* path, uid_t owner, gid_t group)
 {
-	return syscall(SYS_CHOWN, path, owner, group);
+	return fchownat(AT_FDCWD, path, owner, group, 0);
+}
+
+int lchown(const char* path, uid_t owner, gid_t group)
+{
+	return fchownat(AT_FDCWD, path, owner, group, AT_SYMLINK_NOFOLLOW);
+}
+
+int fchown(int fildes, uid_t owner, gid_t group)
+{
+	return fchownat(fildes, nullptr, owner, group, 0);
+}
+
+int fchownat(int fd, const char* path, uid_t owner, gid_t group, int flag)
+{
+	return syscall(SYS_FCHOWNAT, fd, path, owner, group, flag);
 }
 
 void sync(void)