Two changes to AnalysisConsumer::HandleTopLevelSingleDecl():

(1) Since CXXMethodDecl subclasses FunctionDecl (and CXXDestructorDecl 
and CXXConversion subclass CXXMethodDecl), refactor switch statement 
to handle them all in one spot.

(2) Use 'DeclarationName::getAsString()' to handle all functions that
don't have simple identifiers (fixing a null dereference when scanning
for specific functions).

llvm-svn: 96146