VM: always use undecorated names when loading ffi functions

VM: always use undecorated names when loading ffi functions

For win32, Factor tries four different function names when loading
stdcall and fastcall functions, in case decorated names are used in the
dll. It seems to not be necessary because a dll meant for 3rd party use
will always export undecorated
names (http://blogs.msdn.com/b/oldnewthing/archive/2004/01/12/57833.aspx).