add 64bit support to those formats which I could test and which support 64bit build...

add 64bit support to those formats which I could test and which support 64bit build modes (msvc, msvs2005prj and msvs2008prj) by adding a TARGET_CPU option similar to what wxWidgets bakefiles do (note the absence of the WX_ prefix since it does not make sense to have a wx-specific architecture); this additional feature allows correct inclusion of the vc_[amd64|ia64]_[lib|dll] path when building a wx-based project on Windows.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@63608 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775