Don't return but _exit after failed exec*() and fork()

Quoting POSIX[0]:
"Care should be taken, also, to call _exit() rather than exit() if exec cannot be used, since
exit() flushes and closes standard I/O channels, thereby damaging the parent process' standard
I/O data structures. (Even with fork(), it is wrong to call exit(), since buffered data would
then be flushed twice.)"

[0]: http://pubs.opengroup.org/onlinepubs/009695399/functions/vfork.html

xargs.c

@@ -168,13 +168,15 @@ spawn(void)
 	int savederrno;
 
 	pid = fork();
-	if (pid < 0)
-		eprintf("fork:");
+	if (pid < 0) {
+		weprintf("fork:");
+		_exit(1);
+	}
 	if (pid == 0) {
 		execvp(*cmd, cmd);
 		savederrno = errno;
 		weprintf("execvp %s:", *cmd);
-		_exit(savederrno == ENOENT ? 127 : 126);
+		_exit(126 + (savederrno == ENOENT));
 	}
 	waitchld();
 }