Triggered by RT#3989.

(Imported from upstream's fbab8badde. This
doesn't seem to affect us, but avoid getting out of sync.)

Change-Id: I164e2a72e4b75e286ceaa03745ed9bcbf6c3e32e
Reviewed-on: https://boringssl-review.googlesource.com/6512
Reviewed-by: Adam Langley <agl@google.com>