https://rgbds.gbdev.io/install/source currently says that to build RGBDS you need "A C compiler, typically gcc or clang"; and that "If you are building RGBGFX", then you also need "A C++ compiler, typically g++ or clang++" and "libpng's development headers". Two problems with this:

1. Everything is in C++ now.
2. RGBGFX has been one of four core programs for a long time now; people don't build "everything in RGBDS except RGBGFX". Its requirements should be listed with the others so they're harder to miss, perhaps with a note after the list saying what you don't need if you're not building RGBGFX.