feat: attempt to support Gradle 8

This is incomplete and does not fully work yet. We might have to get rid of the lazy configuration of `forkOptions.executable`. See gradle/gradle#23990 (comment)

See #9

src/main/kotlin/io/github/themrmilchmann/gradle/ecj/plugins/ECJPlugin.kt

@@ -30,6 +30,7 @@ import org.gradle.api.tasks.Classpath
 import org.gradle.api.tasks.compile.*
 import org.gradle.jvm.toolchain.*
 import org.gradle.process.CommandLineArgumentProvider
+import org.gradle.util.GradleVersion
 
 public class ECJPlugin : Plugin<Project> {
 
@@ -49,6 +50,8 @@ public class ECJPlugin : Plugin<Project> {
         /* The version required to run ECJ. */
         const val REQUIRED_JAVA_VERSION = 11
 
+        private val GRADLE_8_0 = GradleVersion.version("8.0")
+
     }
 
     override fun apply(target: Project): Unit = applyTo(target) project@{
@@ -77,11 +80,13 @@ public class ECJPlugin : Plugin<Project> {
         val javaToolchains = extensions.getByType(JavaToolchainService::class.java)
 
         tasks.withType(JavaCompile::class.java).configureEach {
-            /* Overwrite the javaCompiler to make sure that it is not inferred from the toolchain. */
-            javaCompiler.set(provider { null })
+            if (GradleVersion.current() < GRADLE_8_0) {
+                /* Overwrite the javaCompiler to make sure that it is not inferred from the toolchain. */
+                javaCompiler.set(provider { null })
+            }
 
             /* ECJ does not support generating JNI headers. Make sure the property is not used. */
-            options.headerOutputDirectory.set(this@project.provider { null })
+            options.headerOutputDirectory.set(provider { null })
 
             options.isFork = true
             options.forkOptions.jvmArgumentProviders.add(ECJCommandLineArgumentProvider(ecjConfiguration))