tests: Add regression test for Debug impl of raw pointers

Author: Enselic

tests/ui/fmt/ptr-metadata.rs

@@ -0,0 +1,19 @@
+//@ run-pass
+//@ check-run-results
+//@ normalize-stdout: "0x[0-9a-fA-F]+" -> "$$HEX"
+
+use std::fmt::Display;
+
+fn main() {
+    let plain = &mut 777;
+    println!("*mut i32: {:?}", plain as *mut i32);
+    println!("*const i32: {:?}", plain as *const i32);
+
+    let slice = &mut [1, 2, 3][..];
+    println!("*mut [i32]: {:?}", slice as *mut [i32]);
+    println!("*const [i32]: {:?}", slice as *const [i32]);
+
+    let vtable = &mut 999 as &mut dyn Display;
+    println!("*mut dyn Display: {:?}", vtable as *mut dyn Display);
+    println!("*const dyn Display: {:?}", vtable as *const dyn Display);
+}

tests/ui/fmt/ptr-metadata.run.stdout

@@ -0,0 +1,6 @@
+*mut i32: $HEX
+*const i32: $HEX
+*mut [i32]: $HEX
+*const [i32]: $HEX
+*mut dyn Display: $HEX
+*const dyn Display: $HEX