Add module-info.java for JPMS support using multi-release JAR

pom.xml

@@ -67,6 +67,40 @@
           </instructions>
         </configuration>
       </plugin>
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-compiler-plugin</artifactId>
+        <!-- defaults for compile and testCompile -->
+        <configuration>
+          <!-- Only required when JAVA_HOME isn't at least Java 9 and when haven't configured the maven-toolchains-plugin -->
+          <jdkToolchain>
+            <version>9</version>
+          </jdkToolchain>
+          <release>8</release>
+        </configuration>
+        <executions>
+          <execution>
+            <id>default-compile</id>
+            <configuration>
+              <!-- compile everything to ensure module-info contains right entries -->
+              <release>9</release>
+            </configuration>
+          </execution>
+          <execution>
+            <id>base-compile</id>
+            <goals>
+              <goal>compile</goal>
+            </goals>
+            <!-- recompile everything for target VM except the module-info.java -->
+            <configuration>
+              <release>8</release>
+              <excludes>
+                <exclude>module-info.java</exclude>
+              </excludes>
+            </configuration>
+          </execution>
+        </executions>
+      </plugin>
       <plugin>
         <groupId>org.apache.maven.plugins</groupId>
         <artifactId>maven-scm-publish-plugin</artifactId>

src/main/java/module-info.java

@@ -0,0 +1,9 @@
+module org.codehaus.plexus.interpolation {
+    exports org.codehaus.plexus.interpolation;
+    exports org.codehaus.plexus.interpolation.fixed;
+    exports org.codehaus.plexus.interpolation.multi;
+    exports org.codehaus.plexus.interpolation.object;
+    exports org.codehaus.plexus.interpolation.os;
+    exports org.codehaus.plexus.interpolation.reflection;
+    exports org.codehaus.plexus.interpolation.util;
+}