Use E0665 for missing `#[default]` error

Use orphaned error code for the same error it belonged to before.

```
error[E0665]: `#[derive(Default)]` on enum with no `#[default]`
  --> $DIR/macros-nonfatal-errors.rs:42:10
   |
LL |   #[derive(Default)]
   |            ^^^^^^^
LL | / enum NoDeclaredDefault {
LL | |     Foo,
LL | |     Bar,
LL | | }
   | |_- this enum needs a unit variant marked with `#[default]`
   |
   = note: this error originates in the derive macro `Default` (in Nightly builds, run with -Z macro-backtrace for more info)
help: make this unit variant default by placing `#[default]` on it
   |
LL |     #[default] Foo,
   |     ~~~~~~~~~~~~~~
help: make this unit variant default by placing `#[default]` on it
   |
LL |     #[default] Bar,
   |     ~~~~~~~~~~~~~~
```

1 files changed, 3 insertions, 3 deletions

diff --git a/compiler/rustc_builtin_macros/messages.ftl b/compiler/rustc_builtin_macros/messages.ftl
index 87d3d288013..7a31d2a2239 100644
--- a/compiler/rustc_builtin_macros/messages.ftl
+++ b/compiler/rustc_builtin_macros/messages.ftl
@@ -249,9 +249,9 @@ builtin_macros_naked_functions_testing_attribute =
     .label = function marked with testing attribute here
     .naked_attribute = `#[naked]` is incompatible with testing attributes
 
-builtin_macros_no_default_variant = no default declared
-    .help = make a unit variant default by placing `#[default]` above it
-    .suggestion = make `{$ident}` default
+builtin_macros_no_default_variant = `#[derive(Default)]` on enum with no `#[default]`
+    .label = this enum needs a unit variant marked with `#[default]`
+    .suggestion = make this unit variant default by placing `#[default]` on it
 
 builtin_macros_non_abi = at least one abi must be provided as an argument to `clobber_abi`