you're trying to compile a C file (sdlmain.m entrypoint) with a C++98 standard enabled
this doesn't make any sense since C++98 is a standard for C++, not C, that's what your compiler is telling you
this looks like an error in sconscript, aka not your fault

yeah, this definitely looks like an error in the sconscript, but I don't know how to fix it ... and I don't have a mac to test and know when it's fixed. Maybe I could figure something out ... I know Gravity.cpp is compiled with different flags already, and SDLMain.m just has to be also