Agreed it's broken, we should have a better fix for this -- I don't remember exactly, but IIRC it's something about `AC_PROG_CXX` setting `CXX` to `g++` if it didn't find no compiler at all, and us wanting to fail hard at configure time instead.
Anyway, as a workaround until it gets fixed, you can set `CXXFLAGS` to `-isystem /sysroot/foo` instead of having this in `CXX` itself. --- Reply to this email directly or view it on GitHub: https://github.com/geany/geany/issues/829#issuecomment-165582221
