Build the tests with release=8 whenever it is possible

Fixes eclipse-openj9/openj9#19888

openjdk.test.mauve/build.xml

@@ -106,10 +106,11 @@ limitations under the License.
  <exclude name="/junit/textui/*.java" />
  </depend>
  -->
- <!-- The test cases are built with source="1.8" and target="1.8" because they need packages
- which have been moved into madules which are not visible by default in Java 9. -->
+ <!-- The test cases are built with release="8" if supported by the compiler, otherwise with
+ source="1.8" and target="1.8" because they need packages. -->
  <javac srcdir="${openjdk_test_mauve_src_dir}"
  destdir="${openjdk_test_mauve_src_dir}"
+ release="8"
  source="1.8"
  target="1.8"
  fork="true"
@@ -124,6 +125,23 @@ limitations under the License.
  <exclude name="**/junit/framework/*.java" />
  <exclude name="/junit/runner/*.java" />
  <exclude name="/junit/textui/*.java" />
+ <exclude name="**/gnu/testlet/java/lang/Class/classInfo/getDeclaredMethod.java" />
+ </javac>
+ <!-- The file gnu/testlet/java/lang/Class/classInfo/getDeclaredMethod.java is built with
+ source="1.8" and target="1.8" because it requires sun.reflect.annotation.AnnotationType
+ that is in module not visible by default in Java 9 and later when using release=8. -->
+ <javac srcdir="${openjdk_test_mauve_src_dir}"
+ destdir="${openjdk_test_mauve_src_dir}"
+ source="1.8"
+ target="1.8"
+ fork="true"
+ executable="${java_compiler}"
+ classpathref="project.class.path"
+ debug="true"
+ encoding="${src-encoding}"
+ includeantruntime="false"
+ failonerror="true">
+ <include name="**/gnu/testlet/java/lang/Class/classInfo/getDeclaredMethod.java" />
  </javac>
  </target>