ClangTools: Allow selecting diagnostic config for project

When starting the Clazy/Tidy tool, allow to select the diagnostic
configuration for the run.

As a side effect, fix a race condition where the runner could end up
with no diagnostic config (removed during run) - copy the diagnostic
config instead of referencing/querying it by the id.

Change-Id: Iedafa8f31a3bbd233d65818fe8de16add1e4d443
Reviewed-by: Ivan Donchevskii <ivan.donchevskii@qt.io>

src/plugins/clangtools/clangselectablefilesdialog.h

@@ -27,6 +27,8 @@
 
 #include "clangfileinfo.h"
 
+#include <coreplugin/id.h>
+
 #include <QDialog>
 
 #include <memory>
@@ -60,6 +62,7 @@ private:
     std::unique_ptr<Ui::SelectableFilesDialog> m_ui;
     std::unique_ptr<SelectableFilesModel> m_filesModel;
 
+    Core::Id m_customDiagnosticConfig;
     ProjectExplorer::Project *m_project;
     QPushButton *m_analyzeButton = nullptr;
 };