Replace obsolete wait3 by waitpid

--- a/src/main.c
+++ b/src/main.c
@@ -193,8 +193,8 @@
 /* handler for reaping children after the fork is done. */
 void handle_child_signal()
 {
-    union wait status;
-    while (wait3(&status, WNOHANG, 0) > 0) {} 
+    int status;
+    while (waitpid(-1, &status, WNOHANG) > 0) {} 
 }
 
 /* handler for HUP. reloads the config file. */