Describe the feature and motivation

I use waikeyEx (or pollkey) in my program. On windows page up key code is 0x210000, In wsl2 key code is 0x10ff55.
i don't know how to define PAGE_UP key because I cannot check system at compile time.
Of course it's possible to add a constant in cmake file and use this constant in source code but I don't want to do that.

My request is
Add
#cmakedefine HAVE_WIN32UI
#cmakedefine HAVE_GTK
#cmakedefine HAVE_COCOA
#cmakedefine HAVE_WAYLAND
in cvconfig.h.in
then at compile time GUI will be known

Additional context

No response