: void *ruby_xcalloc(long n, long size) 
    ֤ͤ calloc() ƱǤ
    Ƥ˼ԤȤ
    GC ԤǤʤȤ㳰 NoMemoryError ȯޤ
    Ĥޤꤳδؿ֤֤ͤȤϾ˳ƤǤ

