Win: Add support for building the C++ dwtestoo with Visual C. Need to use dwmain() macro instead of standard main() entrypoint for Windows. Had to move the _dw_convertargs() definition outside of the dwmain() macro. The macro can be called from C++ code changing the function definition.

[Desktop Entry]
Name=Dynamic Windows Test
Exec=@prefix@/bin/dwtest 
Terminal=false
MultipleArgs=false
Type=Application
Categories=Application;Development;X-Red-Hat-Base;