This is a follow-up to commit b120f5e38d9c (avoid fork-unsafe arc4random implementations, 2018-09-04). Avoid defining a no-op fill_random_bytes_syscall() if arc4random_buf(3) exists, but we are unsure if it is fork-safe. Check for other options instead. IOW, see if getrandom(2) is available. glibc 2.36, released in 2022, started to provide arc4random_buf(3) on Linux. This causes fill_random_bytes_syscall() to use neither of them and makes Random.urandom solely rely on getentropy(3) via fill_random_bytes_urandom(). While the glibc implementation is safe, I did not add it to the list because using getrandom(2) directly is preferable on Linux.