Tried to replace include/vdr and include/libsi by headers from the vdr-dev in the Makefile:
include-dir: -@mkdir -p include/vdr -@(cd include/vdr; for i in ../../*.h; do ln -fs $$i .; done) -@mkdir -p include/libsi -@(cd include/libsi; for i in ../../libsi/*.h; do ln -fs $$i .; done) +@mkdir -p include +@ln -s /usr/include/vdr include/vdr +@ln -s /usr/include/libsi include/libsi
But it didn't help. Plugins are built but they are still binary incompatible.
So, I see only one way to build plugins with headers - debianize them :)