Fix invalid special casing of the unreachable! macro

src/test/ui/macros/unreachable-format-args.rs

@@ -0,0 +1,14 @@
+// ignore-emscripten no processes
+
+// revisions: edition_2015 edition_2021
+// [edition_2015]edition:2015
+// [edition_2021]edition:2021
+// [edition_2015]check-fail
+// [edition_2021]run-fail
+// [edition_2015]error-pattern:there is no argument named `x`
+// [edition_2021]error-pattern:internal error: entered unreachable code: x is 5 and y is 0
+
+fn main() {
+    let x = 5;
+    unreachable!("x is {x} and y is {y}", y = 0);
+}