Test for wcsftime() in configure as it's not available everywhere.

Test for wcsftime() in configure as it's not available everywhere.

Contrary to the comment in wx/wxcrtbase.h, wcsftime() doesn't seem to be
available under quite all the systems, notably it doesn't seem to be present
in OpenBSD at all, even in the very latest version.

Add a configure test for this function and fall back to our own implementation
if the system doesn't have it.

Closes #12766.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@66446 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775