Support for the getrandom() syscall requires syscall(), SYS_getrandom constant, GRND_NONBLOCK and GRND_RANDOM constants, linux/random.h header, etc.

I don't understand your request. configure doesn't check getrandom() syscall result:

        /* ignore the result, Python checks for ENOSYS and EAGAIN at runtime */
        (void)syscall(SYS_getrandom, buffer, buflen, flags);

I don't see how you can support getrandom() if the host doesn't have all constants to compile the C code. Do you have to hardcode constants?