a7170b0412
check stability of macro invocations I haven't implemented tests yet but this should be a pretty solid prototype. I think as-implemented it will also stability-check macro invocations in the same crate, dunno if we want that or not. I don't know if we want this to go through `rustc::middle::stability` or not, considering the information there wouldn't be available at the time of macro expansion (even for external crates, right?). r? @nrc closes #34079 cc @petrochenkov @durka @jseyfried #38356