RFR: 7903928: update build.gradle to use JDK 23 [v3]

[Chen Liang]

On Wed, 15 Jan 2025 09:48:30 GMT, Athijegannathan Sundararajan <sundar at openjdk.org> wrote:

>> I agree. Especially now that we only have one "master" (tip) version.
>
> Gradle's jdk is set via JAVA_HOME. It is usual have gradle support for the latest JDK to come bit "late". If we call JDK needed for jextract to be "jdk_Home" and the one needed for gradle as "JAVA_HOME", we may be in a situation where jdk_home points latest JDK (say JDK 25) and JAVA_HOME points whatever then latest Gradle supports. Can we keep jextract use specific JDK version for its build/test as a separately distinctly named variable?

I think you can run gradle's Java compilation and the gradle tool with different JDKs; my previous strategy for running JMH through gradle was to define my local openjdk build as `org.gradle.java.home` project property, either set in gradle.properties or passed as `-Porg.gradle.java.home=xx` on command line. `JAVA_HOME` is used to launch the gradle tool, so it cannot be the local openjdk build, which uses a class file format too new for gradle to generate abstract method implementations.

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PR Review Comment: https://git.openjdk.org/jextract/pull/271#discussion_r1916876368