Configure: fix build with -Werror=old-style-definition.

Signed-off-by: Piotr Sikora <piotrsikora@google.com>
diff --git a/auto/feature b/auto/feature
index 1145f28..3561f59 100644
--- a/auto/feature
+++ b/auto/feature
@@ -31,7 +31,7 @@
 $NGX_INCLUDE_UNISTD_H
 $ngx_feature_incs
 
-int main() {
+int main(void) {
     $ngx_feature_test;
     return 0;
 }