Add regression test for assert desugaring change

Using the MCVE reported in RUST-145770.

tests/ui/macros/assert-desugaring-145770.rs

@@ -0,0 +1,22 @@
+//! Regression test for #145770.
+//!
+//! Changing the `assert!` desugaring from an `if !cond {}` to `match` expression is
+//! backwards-incompatible, and may need to be done over an edition boundary or limit editions for
+//! which the desguaring change impacts.
+
+#[derive(Debug)]
+struct F {
+    data: bool
+}
+
+impl std::ops::Not for F {
+  type Output = bool;
+  fn not(self) -> Self::Output { !self.data }
+}
+
+fn main() {
+  let f = F { data: true };
+
+  assert!(f);
+  //~^ ERROR mismatched types
+}

tests/ui/macros/assert-desugaring-145770.stderr

@@ -0,0 +1,14 @@
+error[E0308]: mismatched types
+  --> $DIR/assert-desugaring-145770.rs:20:11
+   |
+LL |   assert!(f);
+   |           ^ expected `bool`, found `F`
+   |
+help: you might have meant to use field `data` whose type is `bool`
+   |
+LL |   assert!(f.data);
+   |            +++++
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0308`.