Fix toolchain jdk override was not working for all modules.

Now it also considers the case when separate tasks toolchain
are configured or module only has java toolchain.

^KT-46972 Fixed

compiler/compiler.version/build.gradle.kts

@@ -7,11 +7,7 @@ plugins {
 
 // This module does not apply Kotlin plugin, so we are setting toolchain via
 // java extension
-java {
-    toolchain {
-        languageVersion.set(JavaLanguageVersion.of(6))
-    }
-}
+configureJavaOnlyToolchain(JdkMajorVersion.JDK_1_6)
 
 val kotlinVersion: String by rootProject.extra