I'm a bit late, but I have got to say that I find the new naming extremely confusing since the entire process of cross-compilation is happening at build-time, so either triple is technically a "build-time triple". In fact, the only things running (if we don't take into account testing which the proposal isn't covering) are on the host, so technically the triples used for choosing host tools would be more appropriately named "run-time triples".