sspi build fix

define away Curl_ntlm_sspi_cleanup() when no windows SSPI build

lib/curl_ntlm_msgs.h

@@ -49,6 +49,8 @@ CURLcode Curl_ntlm_decode_type2_message(struct SessionHandle *data,
 /* This is to clean up the ntlm data structure */
 #ifdef USE_WINDOWS_SSPI
 void Curl_ntlm_sspi_cleanup(struct ntlmdata *ntlm);
+#else
+#define Curl_ntlm_sspi_cleanup(x)
 #endif
 
 /* NTLM buffer fixed size, large enough for long user + host + domain */