There's been some juggling of names between rustls_ffi 0.10.0 and 0.11.0, the mod_tls module fails to build

```
./tls_cert.h:196:11: error: unknown type name 'rustls_client_cert_verifier'
    const rustls_client_cert_verifier **pverifier);
          ^
./tls_cert.h:209:11: error: unknown type name 'rustls_client_cert_verifier_optional'
    const rustls_client_cert_verifier_optional **pverifier);
          ^
tls_cert.c:452:11: error: unknown type name 'rustls_client_cert_verifier'
    const rustls_client_cert_verifier *client_verifier;
          ^                                                                                                                                                                                                     tls_cert.c:453:11: error: unknown type name 'rustls_client_cert_verifier_optional'
    const rustls_client_cert_verifier_optional *client_verifier_opt;
          ^
tls_cert.c:461:9: warning: implicit declaration of function 'rustls_client_cert_verifier_free' is invalid in C99 [-Wimplicit-function-declaration]                                                                      rustls_client_cert_verifier_free(entry->client_verifier);
        ^
tls_cert.c:465:9: warning: implicit declaration of function 'rustls_client_cert_verifier_optional_free' is invalid in C99 [-Wimplicit-function-declaration]                                                             rustls_client_cert_verifier_optional_free(entry->client_verifier_opt);
        ^
tls_cert.c:517:11: error: unknown type name 'rustls_client_cert_verifier'
    const rustls_client_cert_verifier **pverifier)                                                                                                                                                                        ^                                                                                                                                                                                                     tls_cert.c:527:34: warning: implicit declaration of function 'rustls_client_cert_verifier_new' is invalid in C99 [-Wimplicit-function-declaration]
        entry->client_verifier = rustls_client_cert_verifier_new(store);
                                 ^
tls_cert.c:543:11: error: unknown type name 'rustls_client_cert_verifier_optional'
    const rustls_client_cert_verifier_optional **pverifier)
          ^
tls_cert.c:553:38: warning: implicit declaration of function 'rustls_client_cert_verifier_optional_new' is invalid in C99 [-Wimplicit-function-declaration]                                                             entry->client_verifier_opt = rustls_client_cert_verifier_optional_new(store);                                                                                                                                                                ^                                                                                                                                                                          4 warnings and 6 errors generated.
```

From the https://github.com/rustls/rustls-ffi/blob/main/CHANGELOG.md 


    rustls_client_cert_verifier became rustls_allow_any_authenticated_client_verifier and must be constructed from a rustls_allow_any_authenticated_client_builder.
    rustls_client_cert_verifier_optional became rustls_allow_any_anonymous_or_authenticated_client_verifier and must be constructed from a rustls_allow_any_anonymous_or_authenticated_client_builder.

Have they broken the API again?

Looks like it.

Builds OK with rustls_ffi 0.10.0.

I think we skip v0.11.0 and see what new name changes v0.12.0 brings.

@Stefan - would a contribution to update to 0.13.0 be helpful? It may take me a little bit of time & some support.

I heard from Stefan out-of-band and he agreed to help support an update. I will try to start working on this Soon(TM).

I've put up an initial PR updating to rustls-ffi 0.13: https://github.com/apache/httpd/pull/439

I think this bug can be closed. Support is in-tree: https://svn.apache.org/viewvc?view=revision&revision=1917270

Thanks!

Now I can try getting the mod_tls port on FreeBSD