https://isocpp.org/files/papers/P2198R0.html

While writing examples for feature-test usage in freestanding, I discovered how much of a pain it is to detect extensions to freestanding. The above paper makes that detection possible and makes policy recommendations for future papers. In order to fix the problem, I ended up bumping the version on _all_ the library feature test macros.

Let me know what you think, and then we can figure out if we need an SG10 telecon to discuss this.