Add ICE reproduction for issue rust-lang/rust#79690.

Author: rustbot

ices/79690.rs

@@ -0,0 +1,26 @@
+union Transmute<T: Copy, U: Copy> {
+    t: T,
+    u: U,
+}
+trait Bar {
+    fn bar(&self) -> u32;
+}
+struct Foo {
+    foo: u32,
+    bar: bool,
+}
+impl Bar for Foo {
+    fn bar(&self) -> u32 {
+        self.foo
+    }
+}
+#[derive(Copy, Clone)]
+struct Fat<'a>(&'a Foo, &'static VTable);
+struct VTable {
+    size: Foo,
+}
+const FOO: &Bar = &Foo {
+    foo: 128,
+    bar: false,
+};
+const G: Fat = unsafe { Transmute { t: FOO }.u };