Fix config fail when there is Werror in CC flag

Author: Josh Chen

config

@@ -1,11 +1,11 @@
 ngx_feature="ngx_http_upstream_check_module"
 ngx_feature_name=
 ngx_feature_run=no
-ngx_feature_incs=
+ngx_feature_incs="#include <stdio.h>"
 ngx_feature_path="$ngx_addon_dir"
 ngx_feature_deps="$ngx_addon_dir/ngx_http_upstream_check_module.h"
 ngx_check_src="$ngx_addon_dir/ngx_http_upstream_check_module.c"
-ngx_feature_test="int a;"
+ngx_feature_test='int a=0; printf("%d", a);'
 . auto/feature
 
 if [ $ngx_found = yes ]; then