Target Java 11 when building compiler plugins.

Change-Id: Ie73c82edb003d4531cc39ef96358659a14cd6940

diff --git a/buildSrc/private/src/main/kotlin/androidx/build/AndroidXImplPlugin.kt b/buildSrc/private/src/main/kotlin/androidx/build/AndroidXImplPlugin.kt
index 1bea081..b7805a6 100644
--- a/buildSrc/private/src/main/kotlin/androidx/build/AndroidXImplPlugin.kt
+++ b/buildSrc/private/src/main/kotlin/androidx/build/AndroidXImplPlugin.kt

@@ -60,6 +60,7 @@
 import javax.inject.Inject
 import org.gradle.api.DefaultTask
 import org.gradle.api.GradleException
+import org.gradle.api.JavaVersion.VERSION_11
 import org.gradle.api.JavaVersion.VERSION_17
 import org.gradle.api.JavaVersion.VERSION_1_8
 import org.gradle.api.Plugin
@@ -273,7 +274,9 @@
     ) {
         project.afterEvaluate {
             project.tasks.withType(KotlinCompile::class.java).configureEach { task ->
-                if (extension.type.compilationTarget == CompilationTarget.HOST &&
+                if (extension.type == LibraryType.COMPILER_PLUGIN) {
+                    task.kotlinOptions.jvmTarget = "11"
+                } else if (extension.type.compilationTarget == CompilationTarget.HOST &&
                     extension.type != LibraryType.ANNOTATION_PROCESSOR_UTILS
                 ) {
                     task.kotlinOptions.jvmTarget = "17"
@@ -484,7 +487,12 @@
         // Force Java 1.8 source- and target-compatibility for all Java libraries.
         val javaExtension = project.extensions.getByType<JavaPluginExtension>()
         project.afterEvaluate {
-            if (extension.type.compilationTarget == CompilationTarget.HOST &&
+            if (extension.type == LibraryType.COMPILER_PLUGIN) {
+                javaExtension.apply {
+                    sourceCompatibility = VERSION_11
+                    targetCompatibility = VERSION_11
+                }
+            } else if (extension.type.compilationTarget == CompilationTarget.HOST &&
                 extension.type != LibraryType.ANNOTATION_PROCESSOR_UTILS
             ) {
                 javaExtension.apply {