Don't include the manifest in wx/msw/wx.rc by default for MSVC compiler.

Don't include the manifest in wx/msw/wx.rc by default for MSVC compiler.

The later versions of this compiler don't need it any more, so make it easier
to set up the projects for them at the expense of MSVC 6 and 7 users who will
now need to explicitly define wxUSE_RC_MANIFEST=1 and predefine the
architecture macro (or setup their resource compiler include path to get
wx/msw/rcdefs.h under the lib directory but predefining the architecture is
clearly simpler).

Do generate manifest when using gcc as it predefines the architecture macros
allowing us to avoid requiring using the generated rcdefs.h.

The other compilers will be dealt with as needed if anybody is still using
them.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@73483 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775