Fix tolower with sanitizer cfi (#208)

Author: bansan85

trantor/net/TcpClient.cc

@@ -238,7 +238,7 @@ void TcpClient::enableSSL(
         std::transform(hostname.begin(),
                        hostname.end(),
                        hostname.begin(),
-                       tolower);
+                       [](unsigned char c) { return tolower(c); });
         SSLHostName_ = std::move(hostname);
     }
 

trantor/net/inner/TcpConnectionImpl.cc

@@ -554,7 +554,7 @@ void TcpConnectionImpl::startClientEncryption(
         std::transform(hostname.begin(),
                        hostname.end(),
                        hostname.begin(),
-                       tolower);
+                       [](unsigned char c) { return tolower(c); });
         assert(sslEncryptionPtr_ != nullptr);
         sslEncryptionPtr_->hostname_ = hostname;
     }