When BoringSSL is imported elsewhere, it would be nice for the links to
be relative, but I'm not sure if that'll work on Gerrit. This change
will try it and can be reverted if
https://boringssl.googlesource.com/boringssl breaks.

Change-Id: I17e056331677923b76fb8852ce8c00e2a4674af4
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/55685
Reviewed-by: David Benjamin <davidben@google.com>
Commit-Queue: Adam Langley <agl@google.com>