=jdk9,str JDK9 ready classes, in special directories (#23650)

* =jdk9,str JDK9 ready classes, in special directories

* =str,jdk9 prepare for releasing using JDK9 (needs sbt 1.0+ though)

* =str,jdk9 passing TCK spec touching some JDK9 types internally

* make sure to include linting options

project/Jdk9CompileDirectoriesPlugin.scala

@@ -0,0 +1,47 @@
+/*
+ * Copyright (C) 2017 Lightbend Inc. <http://www.lightbend.com/>
+ */
+import java.io.File
+
+import sbt._
+import sbt.Keys._
+
+object Jdk9CompileDirectoriesPlugin extends AutoPlugin {
+
+  val jdkVersion: String = System.getProperty("java.version")
+    
+  override def trigger = allRequirements
+
+  override lazy val projectSettings = Seq(
+
+    javacOptions in Compile ++= {
+      // making sure we're really targeting 1.8
+      if (isJDK9) Seq("-target", "1.8", "-source", "1.8", "-Xdoclint:none")
+      else Seq("-Xdoclint:none")
+    },
+    
+    unmanagedSourceDirectories in Compile ++= {
+      if (isJDK9) {
+        println(s"[JDK9] Enabled [...-jdk9-only] directories to be compiled.")
+        Seq(
+          (sourceDirectory in Compile).value / "java-jdk9-only",
+          (sourceDirectory in Compile).value / "scala-jdk9-only"
+        )
+      } else Seq.empty
+    },
+    
+    unmanagedSourceDirectories in Test ++= {
+      if (isJDK9) {
+        Seq(
+          (sourceDirectory in Test).value / "java-jdk9-only",
+          (sourceDirectory in Test).value / "scala-jdk9-only"
+        )
+      } else Seq.empty
+    }
+    
+  )
+
+  private def isJDK9 = {
+    jdkVersion startsWith "9"
+  }
+}