Kernel/LibC: Implement fchmod

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

@@ -55,6 +55,7 @@ __BEGIN_DECLS
 	O(SYS_TTY_CTRL,			tty_ctrl)		\
 	O(SYS_POWEROFF,			poweroff)		\
 	O(SYS_CHMOD,			chmod)			\
+	O(SYS_FCHMOD,			fchmod)			\
 	O(SYS_CREATE,			create)			\
 	O(SYS_CREATE_DIR,		create_dir)		\
 	O(SYS_UNLINK,			unlink) 		\

userspace/libraries/LibC/sys/stat.cpp

@@ -13,9 +13,9 @@ int chmod(const char* path, mode_t mode)
 	return syscall(SYS_CHMOD, path, mode);
 }
 
-int fchmod(int, mode_t)
+int fchmod(int fildes, mode_t mode)
 {
-	ASSERT_NOT_REACHED();
+	return syscall(SYS_FCHMOD, fildes, mode);
 }
 
 int fstat(int fildes, struct stat* buf)