This lets us put the SSL_CIPHER table in the data section. For type-checking,
make STACK_OF(SSL_CIPHER) cast everything to const SSL_CIPHER*.

Note that this will require some changes in consumers which weren't using a
const SSL_CIPHER *.

Change-Id: Iff734ac0e36f9e5c4a0f3c8411c7f727b820469c
Reviewed-on: https://boringssl-review.googlesource.com/1541
Reviewed-by: Adam Langley <agl@google.com>