Fix crash when accessing wxThreadInfo during global initialization time.

We can't rely on our own globals being already constructed if we're called
during another global initialization, so use the usual trick with wrapping
them in accessor functions to ensure that they are.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74935 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775