RFR: Fix Optimized builds

[Aleksey Shipilev]

On Mon, 27 Sep 2021 12:13:00 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> The usual trap in Hotspot code is the belief that `ASSERT <=> !PRODUCT`, but that's not actually true. You would not see this in regular release (`!ASSERT`, `PRODUCT`) or fastdebug (`ASSERT`, `!PRODUCT`) builds, but you would see it in optimized (`!ASSERT`, `!PRODUCT`) builds. See for example GHA: https://github.com/shipilev/loom/runs/3717294006?check_suite_focus=true
> 
> The use of `ASSERT` and `PRODUCT` should be consistent to avoid build failures in optimized builds.
> 
> Additional testing:
>  - [x] Linux x86_64 optimized now builds
>  - [x] Linux x86_64 release still builds
>  - [x] Linux x86_64 fastdebug still builds

That said, I can rewrite all `PRODUCT` defines to `ASSERT`/`DEBUG`, if that was the intent. I think the current patch uses `!PRODUCT` and `ASSERT`/`DEBUG` inconsistently, so we can lean into one side more heavily, e.g. drop all `PRODUCT` thingies...

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PR: https://git.openjdk.java.net/loom/pull/69