fix: Added missing header for conftest

Author: airween

Diff for: config

@@ -10,7 +10,8 @@
 
 ngx_feature_name=
 ngx_feature_run=no
-ngx_feature_incs="#include <modsecurity/modsecurity.h>"
+ngx_feature_incs="#include <modsecurity/modsecurity.h>
+#include <stdio.h>"
 ngx_feature_libs="-lmodsecurity"
 ngx_feature_test='printf("hello");'
 ngx_modsecurity_opt_I=