more prep for included-build Gradle plugins

gradle-plugins/builder-plugins/build.gradle.kts

@@ -0,0 +1,24 @@
+import org.jetbrains.kotlin.gradle.tasks.KotlinCompile
+
+plugins {
+  `kotlin-dsl`
+  kotlin("jvm") version embeddedKotlinVersion
+}
+
+val gradleJvmTarget = "11"
+
+kotlin {
+  jvmToolchain {
+    (this as JavaToolchainSpec).languageVersion.set(JavaLanguageVersion.of(gradleJvmTarget))
+  }
+}
+
+kotlinDslPluginOptions {
+  jvmTarget.set(gradleJvmTarget)
+}
+
+tasks.withType<KotlinCompile>().configureEach {
+  kotlinOptions {
+    jvmTarget = gradleJvmTarget
+  }
+}