Add std::mem::transmute_copy slice test

Author: nvzqz

library/core/tests/mem.rs

@@ -121,6 +121,11 @@ fn test_transmute_copy_shrink() {
     assert_eq!(0_u8, unsafe { transmute_copy(&0_u64) });
 }
 
+#[test]
+fn test_transmute_copy_slice() {
+    assert_eq!(1, unsafe { transmute_copy(&[1][..]) });
+}
+
 #[test]
 fn test_transmute_copy_unaligned() {
     #[repr(C)]