RFR: 8242490: Upgrade to gcc 9.2 on Linux

[Kevin Rushforth]

On Sat, 18 Apr 2020 15:52:36 GMT, Johan Vos <jvos at openjdk.org> wrote:

>> This is a compiler upgrade on Linux from the current gcc 8.3 compiler to gcc 9.2. This will match a recent upgrade done
>> for JDK 15 -- see [JDK-8241721](https://bugs.openjdk.java.net/browse/JDK-8241721).
>> On a related note, using the gcc 9 compiler produces many (harmless) warnings that will be addressed by
>> [JDK-8241476](https://bugs.openjdk.java.net/browse/JDK-8241476) -- see PR #150.
>> I have run a full build and test using this new compiler.
>
> Works on my development system (didn't test on our build system yet)

I won't integrate this until Monday anyway. If you run into a problem with the actual builds using this compiler, let
me know and I'll hold off further (it's been well-tested on my end).

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PR: https://git.openjdk.java.net/jfx/pull/178