Attempt to fix MSVC6 compilation after the previous commit.

Include <shlobj.h> before our wx/msw/missing.h, otherwise many things were
redefined.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@73345 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775