Sync to current upstream arc4random.

This is actually revision 1.33, which is no longer the latest, but it's
as close to head as we can currently reasonably get. I've also switched
to the OpenBSD getentropy_linux.c implementation of getentropy, lightly
modified to try to report an error on failure.

Bug: 14499627
Change-Id: Ia7c561184b1f366c9bf66f248aa60f0d53535fcb
6 files changed