This change adds the OS-specific routines to get random bytes when using
BoringSSL on Fuchsia. Fuchsia uses the Magenta kernel, which provides
random bytes via a syscall rather than via a file or library function.
Change-Id: I32f858246425309d643d142214c7b8de0c62250a
Reviewed-on: https://boringssl-review.googlesource.com/13140
Reviewed-by: David Benjamin <davidben@google.com>
Commit-Queue: David Benjamin <davidben@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>
