Fix Daylight Saving Time (DST) detection. Previous patch was erroneously
dectecting whether DST is currently in effect for the timezone (TZ) in use
instead of emulating the glibc global daylight variable which is set to 0 if
DST conversions should never be applied for the TZ in use; otherwise non-zero.

PR: 220665
Submitted by: madpilot
MFH: 2017Q3