error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
  --> tests/ui-stable/transmute-mut-alignment-increase.rs:19:39
   |
19 | const INCREASE_ALIGNMENT: &mut AU16 = transmute_mut!(&mut [0u8; 2]);
   |                                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: source type: `AlignOf<[u8; 2]>` (8 bits)
   = note: target type: `MaxAlignsOf<[u8; 2], AU16>` (16 bits)
   = note: this error originates in the macro `$crate::assert_align_gt_eq` which comes from the expansion of the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)