ClangPchManager: Introduce UsedMacroAndSourcesCollector

It's a subset to thesymbols collecter so we try to share some code.

Change-Id: I058eee39289453e205f039b3850c1816f1d8ec1a
Task-number: QTCREATORBUG-21257
Reviewed-by: Ivan Donchevskii <ivan.donchevskii@qt.io>

src/tools/clangrefactoringbackend/source/collectmacrossourcefilecallbacks.h

@@ -70,6 +70,7 @@ public:
         m_sourceFiles.clear();
         m_usedMacros.clear();
         m_fileStatuses.clear();
+        m_sourceDependencies.clear();
     }
 
     const UsedMacros &usedMacros() const