Fix build on Windows.

This broke in a19fc259f05e6ec2df0a55e7a37adc37506d3a91.

Change-Id: Icbdb6c7ed7f1f4906cc9c948ecbd6cfd5a0d7e73
Reviewed-on: https://boringssl-review.googlesource.com/2061
Reviewed-by: Adam Langley <agl@google.com>
1 file changed