[ast] [diag] [sil] add note for unreachable function body

include/swift/AST/DiagnosticsSIL.def

@@ -229,6 +229,7 @@ ERROR(guard_body_must_not_fallthrough,none,
       "'guard' body must not fall through, consider using a 'return' or 'throw'"
       " to exit the scope", ())
 WARNING(unreachable_code,none, "will never be executed", ())
+NOTE(unreachable_code_uninhabited_param_note,none, "the function body will never be executed", ())
 NOTE(unreachable_code_branch,none,
      "condition always evaluates to %select{false|true}0", (bool))
 NOTE(call_to_noreturn_note,none,