build: Set the target JVM to 11

Configure Gradle to build class files compatible with Java 11. This
allows to use the published ORT artifacts also in Projects that use Java
11. Previously, Java 17 was required.

The main use case for this is to be able to build the Analyzer Docker
image for the ORT Server [1] with Java 11 which is required to analyze
Gradle projects that are not compatible with newer Java versions.

Relates to #8249.

[1]: https://github.com/eclipse-apoapsis/ort-server

Signed-off-by: Martin Nonnenmacher <[email protected]>

buildSrc/src/main/kotlin/ort-kotlin-conventions.gradle.kts

@@ -111,8 +111,9 @@ detekt {
 }
 
 val javaVersion = JavaVersion.current()
-val maxKotlinJvmTarget = runCatching { JvmTarget.fromTarget(javaVersion.majorVersion) }
+val jvmSourceCompatibility =  runCatching { JvmTarget.fromTarget(javaVersion.majorVersion) }
     .getOrDefault(enumValues<JvmTarget>().max())
+val jvmTargetCompatibility = JvmTarget.JVM_11
 
 val mergeDetektReportsTaskName = "mergeDetektReports"
 val mergeDetektReports = if (rootProject.tasks.findByName(mergeDetektReportsTaskName) != null) {
@@ -124,7 +125,7 @@ val mergeDetektReports = if (rootProject.tasks.findByName(mergeDetektReportsTask
 }
 
 tasks.withType<Detekt>().configureEach detekt@{
-    jvmTarget = maxKotlinJvmTarget.target
+    jvmTarget = jvmTargetCompatibility.target
 
     dependsOn(":detekt-rules:assemble")
 
@@ -154,8 +155,8 @@ tasks.withType<Detekt>().configureEach detekt@{
 
 tasks.withType<JavaCompile>().configureEach {
     // Align this with Kotlin to avoid errors, see https://youtrack.jetbrains.com/issue/KT-48745.
-    sourceCompatibility = maxKotlinJvmTarget.target
-    targetCompatibility = maxKotlinJvmTarget.target
+    sourceCompatibility = jvmSourceCompatibility.target
+    targetCompatibility = jvmTargetCompatibility.target
 }
 
 tasks.withType<KotlinCompile>().configureEach {
@@ -172,7 +173,7 @@ tasks.withType<KotlinCompile>().configureEach {
     compilerOptions {
         allWarningsAsErrors = true
         freeCompilerArgs.addAll(customCompilerArgs)
-        jvmTarget = maxKotlinJvmTarget
+        jvmTarget = jvmTargetCompatibility
     }
 }