*ring* defined a function named `OPENSSL_memcmp` that did what `CRYPTO_memcmp` does in BoringSSL, and BoringSSL has a different function called `OPENSSL_memcmp`. *ring* doesn't need `OPENSSL_memcmp` so sync the `CRYPTO_memcmp` stuff with BoringSSL. This eliminates unnecessary differences from BoringSSL.