This is a little inconvenient for external users of the test suite. It's
also not very helpful to pass -handshaker-path in build configurations
without a handshaker because there won't be a file there anyway.
Change-Id: I6a8fdcfbbf86288876c4c6fda2a46d32663efb69
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/46244
Reviewed-by: Adam Langley <agl@google.com>