RFR: 8204256: improve jlink error message to report unsupported class file format [v2]

[Mandy Chung]

On Mon, 5 Oct 2020 18:53:52 GMT, Ian Graves <igraves at openjdk.org> wrote:

>> I think for `ResolutionException` and IAE (and possibly `PluginException`), the exception message should be helpful
>> enough to correct for example user-errors and that's why this special catch block.
>> Having another look, I think `FindException` may just fall into the last `Throwable` handler.   The new catch block may
>> not be needed.
>
> I noticed that the `Thorowable` catchall case at the bottom was there, but kept the `FindException` as a distinct block
> because the other exceptions exit with a different error code. Catching the `FindException` at the top level is
> technically not an abnormal termination, but a "normal" error case.  Does this matter all that much?

I agree the normal error exit code is appropriate.  The proposed patch is good.  I will sponsor it.

-------------

PR: https://git.openjdk.java.net/jdk/pull/409