In Winelib, you have to be careful not to say 'unsigned long' where
the API expects ULONG, because Winelib doesn't have the Windows LLP64
nature - its unsigned long is 64 bits, whereas ULONG is 32.
Also, my local Winelib has <dwmapi.h> (used in the new demo-screenshot
system), but doesn't contain some of the definitions inside it. So
I've expanded the cmake test of HAVE_DWMAPI_H so that it actually
checks the things we need, instead of just the existence of the
containing header.
ac3ebcc827