What does the gcc warning "project parameter passing for X changed in GCC 7.1" mean?
That warning is telling you that there was a subtle ABI change (actually a conformance fix) between 6 and 7.1, such that libraries built with 6.x or earlier may not work properly when called from code built with 7.x (and vice-versa). As long as all your C++ code is built with GCC 7.1 or later, you can safely ignore this warning. To disable it, pass -Wno-psabi to the compiler.
For more details on the context of the change, see the GCC 7 changelog, and the associated bug.