add regression test for rust-lang#79494

use MCVE

src/test/rustdoc-ui/issue-79494.rs

@@ -0,0 +1,5 @@
+// only-x86_64-unknown-linux-gnu
+
+#![feature(const_transmute)]
+
+const ZST: &[u8] = unsafe { std::mem::transmute(1usize) }; //~ ERROR cannot transmute between types of different sizes, or dependently-sized types

src/test/rustdoc-ui/issue-79494.stderr

@@ -0,0 +1,12 @@
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> $DIR/issue-79494.rs:5:29
+   |
+LL | const ZST: &[u8] = unsafe { std::mem::transmute(1usize) };
+   |                             ^^^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `usize` (64 bits)
+   = note: target type: `&[u8]` (128 bits)
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0512`.