Prohibit JVM target 1.6

But still compile stdlib, reflect, kotlin.test and scripting runtimes
with JVM target 1.6 to simplify migration from Kotlin 1.6 to 1.7.

 #KT-45165 Fixed

libraries/stdlib/jvm/build.gradle

@@ -63,6 +63,8 @@ dependencies {
     testApi project(':kotlin-test:kotlin-test-junit')
 
     builtins project(':core:builtins')
+
+    kotlinCompilerClasspath project(':libraries:tools:stdlib-compiler-classpath')
 }
 
 jar {