Use getrandom system call on Linux instead of reading from /dev/urandom

[happy5214]

For Linux only, the Linux man pages recommend using the getrandom() system call (found in sys/random.h and introduced in kernel version 3.17) instead of reading from /dev/urandom directly. Reasons include the possibility of /dev being hidden by chroot and the function generally being safer. /dev/urandom is read from in

yafu/ytools/util.c

Line 217 in abc4c09

FILE* rand_device = fopen("/dev/urandom", "r");

.