Update compiler/rustc_hir_typeck/messages.ftl

Co-authored-by: Jubilee <[email protected]>

Author: oli-obk

Diff for: compiler/rustc_hir_typeck/messages.ftl

@@ -142,7 +142,7 @@ hir_typeck_option_result_copied = use `{$def_path}::copied` to copy the value in
 hir_typeck_pass_to_variadic_function = can't pass `{$ty}` into variable arguments
     .suggestion = cast the value to `{$cast_ty}`
     .help = cast the value to `{$cast_ty}`
-    .teach_help = certain types, like `{$ty}`, must be casted before passing them to a variadic function, because of arcane ABI rules dictated by the C standard
+    .teach_help = a `{$ty}` would be cast to `{$cast_ty}` by C's default argument promotion
 
 hir_typeck_remove_semi_for_coerce = you might have meant to return the `match` expression
 hir_typeck_remove_semi_for_coerce_expr = this could be implicitly returned but it is a statement, not a tail expression