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

libraries/reflect/build.gradle.kts

@@ -20,11 +20,7 @@ plugins {
     java
 }
 
-java {
-    toolchain {
-        languageVersion.set(JavaLanguageVersion.of(6))
-    }
-}
+configureJavaOnlyToolchain(JdkMajorVersion.JDK_1_6)
 
 publish()