Have it call native getentropy and fall back as required. Should fix
issues of platforms where libc has getentropy but it is not implemented
in the kernel. Based on github PR#354 from simsergey.
This brings us up to current, including djm's random-reseeding change,
as prompted by logan at cyberstorm.mu in bz#3467. It brings the
platform-specific hooks from LibreSSL Portable, simplified to match our
use case. ok djm@.
Since arc4random seeds from getentropy, and we use OpenSSL for that
if enabled, there's the possibility that if we build on a system that
does not have getentropy then run on a system that does have it, then
OpenSSL could end up calling our getentropy and getting stuck in a loop.
Pointed out by deraadt@, ok djm@
Factor out the arc4random seeding into its own file and change the
interface to match getentropy. Use native getentropy if available.
This will make it easier to resync OpenBSD changes to arc4random.
Prompted by bz#3467, ok djm@.
Disables and removes dependency on OpenSSL. Many features don't
work and the set of crypto options is greatly restricted. This
will only work on system with native arc4random or /dev/urandom.
Considered highly experimental for now.
