Migrate repo to use JVM toolchains Gradle feature.

^KT-46972 Fixed

libraries/reflect/api/build.gradle

@@ -2,7 +2,8 @@ description = ''
 
 apply plugin: 'kotlin'
 
-configureJvm6Project(project)
+JvmToolchain.configureJvmToolchain(project, JdkMajorVersion.JDK_1_6)
+LibrariesCommon.disableDeprecatedJvmTargetWarning(project)
 
 def includeJava9 = BuildPropertiesExtKt.getIncludeJava9(project.kotlinBuildProperties)
 
@@ -32,8 +33,9 @@ dependencies {
 }
 
 if (includeJava9) {
-    compileJava9Sources(
-            project, 'kotlin.reflect',
+    LibrariesCommon.configureJava9Compilation(
+            project,
+            'kotlin.reflect',
             [sourceSets.main.output, configurations.compileOnly.filter {
                 !it.name.contains("kotlin-stdlib")
             }]

libraries/reflect/build.gradle.kts

@@ -20,9 +20,11 @@ plugins {
     java
 }
 
-val JDK_16: String by rootProject.extra
-
-callGroovy("configureJavaOnlyJvm6Project", project)
+java {
+    toolchain {
+        languageVersion.set(JavaLanguageVersion.of(6))
+    }
+}
 
 publish()
 
@@ -150,9 +152,19 @@ val proguard by task<CacheableProguardTask> {
     injars(mapOf("filter" to "!META-INF/**,!**/*.kotlin_builtins"), proguardAdditionalInJars)
     outjars(proguardOutput)
 
-    jdkHome = File(JDK_16)
+    javaLauncher.set(project.getToolchainLauncherFor(JdkMajorVersion.JDK_1_6))
     libraryjars(mapOf("filter" to "!META-INF/versions/**"), proguardDeps)
-    libraryjars(firstFromJavaHomeThatExists("jre/lib/rt.jar", "../Classes/classes.jar", jdkHome = jdkHome!!))
+    libraryjars(
+        project.files(
+            javaLauncher.map {
+                firstFromJavaHomeThatExists(
+                    "jre/lib/rt.jar",
+                    "../Classes/classes.jar",
+                    jdkHome = it.metadata.installationPath.asFile
+                )
+            }
+        )
+    )
 
     configuration("$core/reflection.jvm/reflection.pro")
 }