Yields a nice reduction in code size.
Old Go versions miss cipher.NewGCMWithNonceSize, which causes: internal/speed/speed.go:95: undefined: cipher.NewGCMWithNonceSize
A crypto benchmark mode like "openssl speed". Example run: $ ./gocryptfs -speed AES-GCM-256-OpenSSL 180.89 MB/s (selected in auto mode) AES-GCM-256-Go 48.19 MB/s AES-SIV-512-Go 37.40 MB/s