Extend time_t-based handling all the way to the end of time_t

At least some modern 64-bit systems have widened time_t to 64 bits
fixing the "Unix time" problem. (This is even the default on MS-Win,
although the system functions artificially limit the accepted range to
1970 through 3000.) Even the 32-bit range extends into January 2038
but the code was artificially cutting this off at the end of 2037.
This is a preparation for using the same also all the way back to the
start of time_t.

In the process, simplify and tidy up the logic of the existing code,
update the docs (this includes correcting some misinformation) and
revise some tests.

Fixes: QTBUG-73225
Change-Id: Ib8001b5a982386c747eda3dea2b5a26eedd499ad
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

0 files changed, 0 insertions, 0 deletions