Add and update more tests

Author: oli-obk

src/test/ui/consts/miri_unleashed/mutable_references_ice.stderr

@@ -7,7 +7,7 @@ LL |         *MUH.x.get() = 99;
 thread 'rustc' panicked at 'assertion failed: `(left != right)`
   left: `Const`,
  right: `Const`: UnsafeCells are not allowed behind references in constants. This should have been prevented statically by const qualification. If this were allowed one would be able to change a constant at one use site and other use sites may arbitrarily decide to change, too.', src/librustc_mir/interpret/intern.rs:126:17
-note: Run with `RUST_BACKTRACE=1` environment variable to display a backtrace.
+note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace.
 
 error: internal compiler error: unexpected panic
 

src/test/ui/consts/packed_pattern2.rs

@@ -0,0 +1,27 @@
+// run-pass
+
+#[derive(PartialEq, Eq, Copy, Clone)]
+#[repr(packed)]
+struct Foo {
+    field: (u8, u16),
+}
+
+#[derive(PartialEq, Eq, Copy, Clone)]
+#[repr(align(2))]
+struct Bar {
+    a: Foo,
+}
+
+const FOO: Bar = Bar {
+    a: Foo {
+        field: (5, 6),
+    }
+};
+
+fn main() {
+    match FOO {
+        Bar { a: Foo { field: (5, 6) } } => {},
+        FOO => unreachable!(),
+        _ => unreachable!(),
+    }
+}