Appease the Chromium build on OS X.

Change-Id: Idb7466b4d3e4cc9161cd09066b2f79a6290838b1
Reviewed-on: https://boringssl-review.googlesource.com/1240
Reviewed-by: Adam Langley <agl@google.com>

(Imported from upstream's ca88a1d439)

(Imported from upstream's 5615196f7bd467f1e56e275bf740a62caa04d107.)

Initial fork from f2d678e6e8 (1.0.2 beta).

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