More malloc failure stuff.

Change-Id: I9c34941cbf43919b501a4a737ff150e4e2606949
Reviewed-on: https://boringssl-review.googlesource.com/4519
Reviewed-by: Adam Langley <agl@google.com>

Initial fork from f2d678e6e8 (1.0.2 beta).

(This change contains substantial changes from the original and
effectively starts a new history.)