add riscv64 architecture support

[musl] / arch / riscv64 / bits / sem.h

struct semid_ds {
        struct ipc_perm sem_perm;
        time_t sem_otime;
        time_t sem_ctime;
        unsigned short sem_nsems;
        char __sem_nsems_pad[sizeof(time_t)-sizeof(short)];
        time_t __unused3;
        time_t __unused4;
};