Apologies if this is not the right forum to report this, I'm not really familiar with packaging ecosystem.
Problem: C++ headers shipped with libgeos++-dev package do not include inline files. As a result one can not compile with -DGEOS_INLINE flag. My understanding is that it should be safe to compile with this flag set even if the library was compiled without the flag and hence includes object code for those functions as well.
It looks like all versions are affected, so not sure if this is by design or an omission.