eduke32: fix build

pkgs/games/eduke32/default.nix

···
       --replace libGLU.so	${mesa}/lib/libGLU.so
   '';
 
-  NIX_CFLAGS_COMPILE = "-I${SDL2}/include/SDL";
+  NIX_CFLAGS_COMPILE = "-I${SDL2.dev}/include/SDL2 -I${SDL2_mixer}/include/SDL2";
   NIX_LDFLAGS = "-L${SDL2}/lib";
 
   makeFlags = [