POSIX specifies that tzset() consults environment variable TZ and
modifies some globals; it also specifies mktime(), localtime() and
strftime() to behave as if they called tzset(). Fortunately, we only
call strftime() from a test and only call localtime() when not
threaded. Provide wrappers for tzset() and mktime() that share the
lock used by our environment-access code, to prevent races on the
environment (and tzset()'s globals) when we call them.
In the process, re-use tst_QDateTime's TimeZoneRollback in its older
test systemTimeZoneChange() and presume that this can now be tested
cross-platform, since TimeZoneRollback is used in another test where
this works.
Fixes: QTBUG-71030
Change-Id: I79f559b8857ea2803e73501008bf0d7158c6731f
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
6c543879a3