Fix MinGW build after MSVC6 removal changes.

Don't define wxUSE_DBGHELP as 1 for MinGW, it was only supposed to be defined
as 1 for MSVC (just for all versions of it now that we don't support MSVC6
which couldn't compile this code).

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@76534 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
Remove support for Win9x from wxMSW.

Most importantly, this allows us to remove all MSLU-related stuff.

Some functions which were previously loaded dynamically can now be just used
directly, too.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@76535 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775