It's only used in the autotests, and it private API, so
downgrade from Q_CORE_EXPORT to Q_AUTOTEST_EXPORT.
Fix a use of QTimeZonePrivate functions unprotected by
QT_BUILD_INTERNAL in tst_qtimezone.cpp.
Change-Id: I70eaea06f8fcf2983aeafb6894c3a5d2a4b272a7
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>