LibCore: Add mknod() syscall wrapper

Author: https://github.com/kennethmyhra
Commit: 9fe1ebebdc
Pull-request: https://github.com/SerenityOS/serenity/pull/11896
Reviewed-by: https://github.com/ADKaster
Reviewed-by: https://github.com/alimpfard
Reviewed-by: https://github.com/awesomekling
Reviewed-by: https://github.com/bgianfo ✅
Reviewed-by: https://github.com/linusg

Userland/Libraries/LibCore/System.h

@@ -135,4 +135,6 @@ ErrorOr<void> getsockname(int sockfd, struct sockaddr*, socklen_t*);
 ErrorOr<void> getpeername(int sockfd, struct sockaddr*, socklen_t*);
 ErrorOr<void> socketpair(int domain, int type, int protocol, int sv[2]);
 ErrorOr<Vector<gid_t>> getgroups();
+ErrorOr<void> mknod(StringView pathname, mode_t mode, dev_t dev);
+
 }