Fix OSS QUICHE build.

SSL_get_signature_algorithm_used was introduced when BORINGSSL_API_VERSION was
40, so limit its use to 41+ to ensure it exists.

PiperOrigin-RevId: 948640473

quiche/quic/core/tls_server_handshaker.cc

diff --git a/quiche/quic/core/tls_server_handshaker.cc b/quiche/quic/core/tls_server_handshaker.cc
index b592199..ad694d0 100644
--- a/quiche/quic/core/tls_server_handshaker.cc
+++ b/quiche/quic/core/tls_server_handshaker.cc
@@ -636,8 +636,10 @@
     }
     crypto_negotiated_params_->key_exchange_group = SSL_get_curve_id(ssl());
     crypto_negotiated_params_->encrypted_client_hello = SSL_ech_accepted(ssl());
+#if BORINGSSL_API_VERSION >= 41
     crypto_negotiated_params_->signature_algorithm_used =
         SSL_get_signature_algorithm_used(ssl());
+#endif
   }
   TlsHandshaker::SetWriteSecret(level, cipher, write_secret);
 }