suggest const or static for global variable

compiler/rustc_parse/src/parser/item.rs

@@ -68,7 +68,12 @@ impl<'a> Parser<'a> {
             if !self.maybe_consume_incorrect_semicolon(&items) {
                 let msg = &format!("expected item, found {token_str}");
                 let mut err = self.struct_span_err(self.token.span, msg);
-                err.span_label(self.token.span, "expected item");
+                let label = if self.is_kw_followed_by_ident(kw::Let) {
+                    "consider using `const` or `static` instead of `let` for global variables"
+                } else {
+                    "expected item"
+                };
+                err.span_label(self.token.span, label);
                 return Err(err);
             }
         }