Add toolchain to gradle config file

[dsyer]

This could probably be improved, but it looks to me like it might be needed to persuade the JDT Language Server (used by Eclipse and VSCode) to build the project cleanly.

In VSCode you have to import one of the test projects into the workspace (probably the same in Eclipse). If you do that before this change the build will fail and you won't be able to use the Java language features in the IDE.

With this change if you run with Java 17, but not the GraalVM edition:

$ ./gradlew clean test -Pcoordinates=io.netty:netty-common:4.1.80.Final

> Configure project :
GraalVM Reachability Metadata TCK
---------------------------------

> Task :test-io.netty-netty-common-4.1.80.Final
====================
Testing library: io.netty:netty-common:4.1.80.Final
Command: `/workspaces/graalvm-reachability-metadata/gradlew nativeTest`
Executing test...
-------
Command: [/workspaces/graalvm-reachability-metadata/gradlew, nativeTest]
Starting a Gradle Daemon, 4 busy and 4 incompatible and 6 stopped Daemons could not be reused, use --status for details
> Task :tck-build-logic:extractPluginRequests UP-TO-DATE
> Task :tck-build-logic:generatePluginAdapters UP-TO-DATE
> Task :tck-build-logic:compileJava UP-TO-DATE
> Task :tck-build-logic:compileGroovy UP-TO-DATE
> Task :tck-build-logic:compileGroovyPlugins UP-TO-DATE
> Task :tck-build-logic:pluginDescriptors UP-TO-DATE
> Task :tck-build-logic:processResources UP-TO-DATE
> Task :tck-build-logic:classes UP-TO-DATE
> Task :tck-build-logic:jar UP-TO-DATE
> Task :compileJava NO-SOURCE
> Task :processResources NO-SOURCE
> Task :classes UP-TO-DATE

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':compileTestJava'.
> Error while evaluating property 'javaCompiler' of task ':compileTestJava'
   > Failed to calculate the value of task ':compileTestJava' property 'javaCompiler'.
      > No compatible toolchains found for request filter: {languageVersion=17, vendor=GRAAL_VM, implementation=vendor-specific} (auto-detect true, auto-download true)
...

Without this change it just fails with no indication of how to fix it.

[dsyer]

Fixes #147

[melix]

Unfortunately I think this PR may become the root of other strange issues for users. In particular, using vendor=GRAAL_VM will only work for GraalVM Community Edition. So it means builds would start to fail locally for those using GraalVM EE (or potentially other VMs like Liberica). This is caused by a limitation in Gradle. I'm not quite sure how to reconcile the needs in Eclipse JDT and this :/

[dsyer]

It actually doesn’t work with the Liberica build already. That was one of the reasons I added the vendor label.

[melix]

It actually doesn’t work with the Liberica build already. That was one of the reasons I added the vendor label.

Indeed it seems it works because the vendor reported by Liberica is GraalVM.

[melix]

So we can merge this, but it means that folks trying to make it work with EE will have to manually tweak the build.

[vjovanov]

So we can merge this, but it means that folks trying to make it work with EE will have to manually tweak the build.

CC @dnestoro