Buffer reads of urandom, if you promise no forking.

Callers that lack hardware random may obtain a speed improvement by
calling |RAND_enable_fork_unsafe_buffering|, which enables a
thread-local buffer around reads from /dev/urandom.

Change-Id: I46e675d1679b20434dd520c58ece0f888f38a241
Reviewed-on: https://boringssl-review.googlesource.com/5792
Reviewed-by: Adam Langley <agl@google.com>
6 files changed