The build tool, GenModuleInfoSource, for module-info does not check for duplicate targets in export statements.
By comparison, javac and javadoc check for and report duplicates as errors.

For example, this extract from module-info.java

```
exports jdk.internal.util to
        java.desktop,
        java.net.http,
        java.prefs,
        java.security.jgss,
        java.smartcardio,
        java.naming,
        java.rmi,
        java.net.http,
        jdk.charsets,
        jdk.incubator.vector,
        jdk.internal.vm.ci,
        jdk.httpserver,
        jdk.jlink,
        jdk.jpackage,
        jdk.net;
```