LibC: Make tzset() set daylight to 0

Quoting POSIX:

    https://pubs.opengroup.org/onlinepubs/009695399/functions/tzset.html

    The tzset() function also shall set the external variable daylight
    to 0 if Daylight Savings Time conversions should never be applied
    for the timezone in use; otherwise, non-zero.

We're already pretending to be in UTC+0 and setting timezone to 0
accordingly, we can also fake the absence of Daylight Savings Time.

Userland/Libraries/LibC/time.cpp

@@ -333,6 +333,7 @@ void tzset()
 {
     // FIXME: Here we pretend we are in UTC+0.
     timezone = 0;
+    daylight = 0;
     tzname[0] = const_cast<char*>(__utc);
     tzname[1] = const_cast<char*>(__utc);
 }