Native month calendar functions doesn't always return correct values in the time part of SYSTEMTIME so ignore it and use just the date component. To simplify doing it, add helper (MSW-specific) SetFromMSWSysDate() and GetAsMSWSysDate() functions which convert between wxDateTime and SYSTEMTIME but take only date component into account. This commit partially replaces changes of r63560 and closes #11276. git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@64208 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775