LibCore: Add syscall wrapper for chmod()

Author: https://github.com/kennethmyhra
Commit: 0d76d15f9d
Pull-request: https://github.com/SerenityOS/serenity/pull/11168
Reviewed-by: https://github.com/bgianfo ✅

Userland/Libraries/LibCore/System.h

@@ -41,5 +41,6 @@ ErrorOr<String> gethostname();
 ErrorOr<void> ioctl(int fd, unsigned request, ...);
 ErrorOr<struct termios> tcgetattr(int fd);
 ErrorOr<void> tcsetattr(int fd, int optional_actions, struct termios const&);
+ErrorOr<void> chmod(StringView pathname, mode_t mode);
 
 }