Revert "remove sigchld function"

This reverts commit 1fa72b0772.
Fixes #97.

dwl.c

@@ -278,6 +278,7 @@ static void setlayout(const Arg *arg);
 static void setmfact(const Arg *arg);
 static void setmon(Client *c, Monitor *m, unsigned int newtags);
 static void setup(void);
+static void sigchld(int unused);
 static void spawn(const Arg *arg);
 static void tag(const Arg *arg);
 static void tagmon(const Arg *arg);
@@ -1983,9 +1984,8 @@ setup(void)
 	 * clients from the Unix socket, manging Wayland globals, and so on. */
 	dpy = wl_display_create();
 
-	/* Indicate explicitly to the OS that we are not interested in info
-	 * about child processes (per POSIX.1-2001) */
-	signal(SIGCHLD, SIG_IGN);
+	/* clean up child processes immediately */
+	sigchld(0);
 
 	/* The backend is a wlroots feature which abstracts the underlying input and
 	 * output hardware. The autocreate option will choose the most suitable
@@ -2136,6 +2136,20 @@ setup(void)
 #endif
 }
 
+void
+sigchld(int unused)
+{
+	/* We should be able to remove this function in favor of a simple
+	 *     signal(SIGCHLD, SIG_IGN);
+	 * but the Xwayland implementation in wlroots currently prevents us from
+	 * setting our own disposition for SIGCHLD.
+	 */
+	if (signal(SIGCHLD, sigchld) == SIG_ERR)
+		EBARF("can't install SIGCHLD handler");
+	while (0 < waitpid(-1, NULL, WNOHANG))
+		;
+}
+
 void
 spawn(const Arg *arg)
 {