add some tests with constants that better be valid

src/test/ui/consts/const-eval/valid-const.rs

@@ -0,0 +1,18 @@
+// compile-pass
+
+// Some constants that *are* valid
+#![feature(const_transmute)]
+
+use std::mem;
+use std::ptr::NonNull;
+use std::num::{NonZeroU8, NonZeroUsize};
+
+const NON_NULL_PTR1: NonNull<u8> = unsafe { mem::transmute(1usize) };
+const NON_NULL_PTR2: NonNull<u8> = unsafe { mem::transmute(&0) };
+
+const NON_NULL_U8: NonZeroU8 = unsafe { mem::transmute(1u8) };
+const NON_NULL_USIZE: NonZeroUsize = unsafe { mem::transmute(1usize) };
+
+const UNIT: () = ();
+
+fn main() {}