Ok, that got me a bunch further. (SVN 4229)
Now I have:
g++ -DHAVE_CONFIG_H -I. -I. -I../../../src/include -I/usr/local/lib/wx/include/x11univ-ansi-release-2.8 -I/usr/local/include/wx-2.8 -D_FILE_OFFSET_BITS=64 -D_LARGE_FILES -D__WXUNIVERSAL__ -D__WXX11__ -pthread -I../../../src/include/wxFlatNotebook/include -Ulinux -Uunix -O2 -ffast-math -g -O2 -DCB_PRECOMP -Winvalid-pch -fPIC -DPIC -fexceptions -MT popup_dlg.lo -MD -MP -MF .deps/popup_dlg.Tpo -c src/wxFlatNotebook/popup_dlg.cpp -fPIC -DPIC -o .libs/popup_dlg.o
../../../src/include/wxFlatNotebook/include/wx/wxFlatNotebook/wxFNBDropTarget.h:75: error: invalid use of undefined type ‘struct wxDropTarget’
/usr/local/include/wx-2.8/wx/window.h:60: error: forward declaration of ‘struct wxDropTarget’
../../../src/include/wxFlatNotebook/include/wx/wxFlatNotebook/wxFNBDropTarget.h:78: error: expected identifier before ‘*’ token
wxWidgets-2.8.4 --with-X11 --enable-compat26
codeblocks --with-X11 --enable-contrib
Thanks Tim S for help on the last one.