[google/compile-testing#222] add JVM arg to allow access to compiler internal APIs on Java 16

Author: remkop

picocli-annotation-processing-tests/build.gradle

@@ -21,6 +21,12 @@ dependencies {
         testImplementation files(org.gradle.internal.jvm.Jvm.current().getToolsJar()) // needed on Java 8: https://github.com/google/compile-testing/issues/102 (and #28)
     }
 }
+tasks.withType(Test.class) {
+    if (org.gradle.api.JavaVersion.current().isJava12Compatible()) { // only a problem from Java 16, but okay
+        it.jvmArgs '--add-opens=jdk.compiler/com.sun.tools.javac.api=ALL-UNNAMED' // https://github.com/google/compile-testing/issues/222
+    }
+}
+
 jar {
     manifest {
         attributes 'Specification-Title': 'Picocli Annotation Processing Tests',