[MCOMPILER-423] Unable to define qualified exports to unknown modules without triggering compiler warning

**[Gili](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=cowwoc)** opened **[MCOMPILER-423](https://issues.apache.org/jira/browse/MCOMPILER-423?redirect=false)** and commented

Following up on a discussion with [Karl Heinz Marbaise](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=khmarbaise) at https://stackoverflow.com/q/53670052/14731

It doesn't seem to be possible to compile the attached testcase without triggering a compiler warning.

Expected behavior: Maven compiler plugin should pass --module-source-path to avoid the compiler warning.

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**Affects:** 3.8.1

**Attachments:**
- [qualified-exports-module-source-path.zip](https://issues.apache.org/jira/secure/attachment/13006672/qualified-exports-module-source-path.zip) (_24.52 kB_)

Unpack qualified-exports-module-source-path.zip and reproduce the compiler warning with the attached testcase. Then trace the Maven compiler plugin's module-related compiler argument handling; done means the testcase compiles with --module-source-path passed and without the warning.

Written by the indexing model from the issue text.