We don't really need uniform distribution for mktemp(3) so use

We don't really need uniform distribution for mktemp(3) so use
arc4random_buf() to avoid lots of arc4random() calls with a getpid()
syscall for each one.  We fetch 32 bytes of random data at a time
which can handle up to 16 Xs.  16 Xs should be enough for anyone.
Requested and OK deraadt@