Add support for 3DES ECB.

At least the linker can discard this function in the cases where nobody
is calling it.

Change-Id: I30050e918e6bc1dd9c97cc70f3a56408701abebc
Reviewed-on: https://boringssl-review.googlesource.com/3724
Reviewed-by: Adam Langley <agl@google.com>
2 files changed