The FreeBSD-native arc4random_buf implementation falls back to weak
sources of entropy if the sysctl fails. Remove these dangerous fallbacks
by overriding locally.
Unfortunately, pthread_atfork() is broken on FreeBSD (at least 9 and 10)
if a program does not link to -lthr. Callbacks registered with
pthread_atfork() simply fail silently. So, it is not always possible to
detect a PID wraparound. I wish we could do better.
This improves arc4random_buf's safety compared to the native FreeBSD
implementation. Tested on FreeBSD 9 and 10.
ok beck@ deraadt@
Simplify autoconf checks by using AC_CHECK_FUNCS/HEADERS.
Clarify some ambiguous dependencies around strnlen/strndup.
Unconditionally enable pidwraptest for all arc4random implementations.
Remove HAVE_VASPRINTF conditional, since asprintf requires vasprintf.
ok @doug
