Userland: Add missing limits.h header includes

This is currently being implicitly including by InodeWatcherEvent.h by
way of FileWatcher.h. The former will soon be removed from the latter,
which would otherwise cause a compile error in these files.

Userland/Libraries/LibCore/FileWatcherLinux.cpp

@@ -11,6 +11,7 @@
 #include <Kernel/API/InodeWatcherFlags.h>
 #include <LibCore/Notifier.h>
 #include <errno.h>
+#include <limits.h>
 #include <string.h>
 #include <sys/inotify.h>
 #include <sys/ioctl.h>

Userland/Services/LookupServer/LookupServer.cpp

@@ -16,6 +16,7 @@
 #include <LibCore/LocalServer.h>
 #include <LibCore/Stream.h>
 #include <LibDNS/Packet.h>
+#include <limits.h>
 #include <stdio.h>
 #include <time.h>
 #include <unistd.h>