Prevent the use of windowsx.h with Wine source.

[Mike McCormack]

Robert Shearman wrote:

> Why don't we fix the macros as suggested by Francois, rather than
> preventing its use? It seems like a big waste of time to have submitted
> all of the patches to the files using windowsx.h when fixing the macros
> is necessary for Winelib anyway.

No, it's not a waste of time.  Having warning free Wine source code is 
far more important than any warnings that might be in 3rd party winelib 
code.

Francois' solution is still not perfect, as it requires use of a 
non-portable C construct.

Mike