Use JDK_16 to build pcollections

Author: ilya-g

build.gradle

@@ -0,0 +1,10 @@
+ext.JDK_16 = System.getenv("JDK_16")
+
+project('pcollections') {
+    afterEvaluate {
+        compileJava {
+            options.fork = true
+            options.forkOptions.executable = "${JDK_16}/bin/javac"
+        }
+    }
+}