Fix use-after-release bug introduced in r77585 where the PathDiagnosticClient

Fix use-after-release bug introduced in r77585 where the PathDiagnosticClient
created by AnalysisConsumer would be released by an instance of AnalysisManager
and then reused by later instances of AnalysisManager. Ownership of the
PathDiagnosticClient now belongs (for now) in AnalysisConsumer.

We also need this layering (for now) because the HTMLDiagnostiClient requires
that the entire translation unit be processed before emitting diagnostics. This
is done in its destructor (which should also be fixed, but that is another
issue).

This fixes PR 4653.

llvm-svn: 77648