Reword note

compiler/rustc_parse/messages.ftl

@@ -189,7 +189,7 @@ parse_dotdotdot = unexpected token: `...`
 parse_dotdotdot_rest_pattern = unexpected `...`
     .label = not a valid pattern
     .suggestion = for a rest pattern, use `..` instead of `...`
-    .note = C-variadic type `...` is not allowed here
+    .note = only `extern "C"` and `extern "C-unwind"` functions may have a C variable argument list
 
 parse_double_colon_in_bound = expected `:` followed by trait or lifetime
     .suggestion = use single colon

tests/ui/c-variadic/no-closure.stderr

@@ -10,7 +10,7 @@ error: unexpected `...`
 LL |     let f = |...| {};
    |              ^^^ not a valid pattern
    |
-   = note: C-variadic type `...` is not allowed here
+   = note: only `extern "C"` and `extern "C-unwind"` functions may have a C variable argument list
 
 error[E0743]: C-variadic type `...` may not be nested inside another type
   --> $DIR/no-closure.rs:13:17