Changed lint to check for std::fmt::Pointer and transmute

The lint checks arguments in calls to `transmute` or functions that have
`Pointer` as a trait bound and displays a warning if the argument is a function
reference. Also checks for `std::fmt::Pointer::fmt` to handle formatting macros
although it doesn't depend on the exact expansion of the macro or formatting
internals. `std::fmt::Pointer` and `std::fmt::Pointer::fmt` were also added as
diagnostic items and symbols.

compiler/rustc_span/src/symbol.rs

@@ -796,6 +796,8 @@ symbols! {
         plugin_registrar,
         plugins,
         pointer,
+        pointer_trait,
+        pointer_trait_fmt,
         poll,
         position,
         post_dash_lto: "post-lto",