Redefine IAutoCompleteDropDown in our code as it's not always available.

Redefine IAutoCompleteDropDown in our code as it's not always available.

MinGW doesn't have shobjidl.h header file which is normally part of the
Platform SDK and doesn't have IAutoCompleteDropDown interface definition in
any of its headers at all, so define this interface and its IID ourselves to
make the code compile with it.

Notice that MinGW-64 does have the interface declaration but still doesn't
define IID_IAutoCompleteDropDown.

So to be on the safe side just always define everything ourselves, as long as
we need to do it for one of the compilers, it's not more difficult to do it
for all of them.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@67567 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775