At this point, it's not realistic to maintain interesting C++ programs without a build system. That being said, I expect the specific g++ example you provide will end up working with some special casing in the compiler, at least eventually, when someone submits patches to GCC to get it to work.
But mostly, it's not realistic to directly wire up calls to g++ anymore outside of research examples. Note that other compiled languages use systems like gobuild, cargo, Maven, etc. instead of fiddling with gccgo, rustc, javac, etc. directly.
I think your point is orthogonal to OP's point. I agree with him, the first chapter of a book about a programming language should include hello world and it should ruthlessly minimise barriers to the broadest range of possible readers being able to try that out. They can then supplement their reading with active experimentation, a vital step. You can't learn to swim by reading a book about swimming.
But mostly, it's not realistic to directly wire up calls to g++ anymore outside of research examples. Note that other compiled languages use systems like gobuild, cargo, Maven, etc. instead of fiddling with gccgo, rustc, javac, etc. directly.
https://www.kitware.com/import-std-in-cmake-3-30/