Is your feature request related to a problem? Please describe.
This is about type resolution and the configured auxclasspath. In case the auxclasspath is incomplete or missing, PMD wouldn't work correctly, e.g. reporting false positives / false negatives.

Describe the solution you'd like
Report any classes that are missing on the auxclasspath during analysis. If these classes are reported e.g. as "processing errors" (I know, we trying to renaming these to recoverable errors, but missing class is not recoverable in general), other tools like maven could fail the build based on that.

Describe alternatives you've considered
?

Additional context

• See the problem here: [MPMD-399] Incorrect warning: The project X does not seem to be compi… apache/maven-pmd-plugin#154 (review)
• And [java] matchesSig does not match some signatures that it should #6113
• And Inidcate unresolved imports pmd-designer#258
• And [java] UnusedPrivateMethod: False positive with overloaded private methods called with values returned from methods defined in other classes #6393
• And [java] CloneMethodMustImplementCloneable: False positive when Cloneable is a super interface #6345
• And Rule: EnumComparison in a multi-module project #6418