Add AMII_PALETTE_SIZE / AMIV_PALETTE_SIZE in amiconf.h to make the
actual populated portion of the init-map arrays explicit. Drop the
redundant extern void exit() declaration. Annotate Abort with
NORETURN in both amiconf.h and winproto.h; drop the duplicate Abort
declaration further down winproto.h.
Convert the bare-token "CLIPPING must be defined" assertion in
windefs.h into a real #error directive.
Comment in winext.h to disambiguate the three similarly named
amii*_init*map palette arrays.