Thank you Ian, hopefully I will be compatible then for a long time, as Larry Wall would say "at least until the heat death of the Universe".
I can't "ignore it" :) My build system cannot handle "include_next" - it cannot handle the situation where you are finding a header file in one -I directory, and later when you are trying to find it again, you ignore that directory and find it in a subsequent -I directory. The system is extremely fast, like a sports car than will only go on asphalt (standard C and a GCC-like compiler). >I recommend that you simply ignore it in your build system.