Adds real_server_signature symbol to msc_test

Missing symbol was leading the tests to fail

Author: Felipe Zimmerle

tests/msc_test.c

@@ -77,6 +77,7 @@ static unsigned char buf[BUFLEN];
 msc_engine *modsecurity = NULL;
 unsigned long int DSOLOCAL msc_pcre_match_limit = 0;
 unsigned long int DSOLOCAL msc_pcre_match_limit_recursion = 0;
+char DSOLOCAL *real_server_signature = NULL;
 
 /* Stubs */
 char *format_error_log_message(apr_pool_t *mp, error_message_t *em) {