samples: Make fs-monitor depend on libc and headers

Prevent build errors when headers or libc are not available, such as on
kernel build bots, like the below:

samples/fanotify/fs-monitor.c:7:10: fatal error: errno.h: No such file
or directory
  7 | #include <errno.h>
    |          ^~~~~~~~~

Link: https://lore.kernel.org/r/87fsslasgz.fsf@collabora.com


Suggested-by: Guenter Roeck <linux@roeck-us.net>
Tested-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.com>
Signed-off-by: Jan Kara <jack@suse.cz>