Clang: Add option 'Build before analysis' to project settings

Diagnostic configuration Id was already there but
not the checkbox whether to build project or not.

Change-Id: Icb5fc15bda5eed5e375cd90df1a96060b30bf57e
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@qt.io>
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@qt.io>

src/plugins/clangtools/clangselectablefilesdialog.h

@@ -65,6 +65,7 @@ private:
     Core::Id m_customDiagnosticConfig;
     ProjectExplorer::Project *m_project;
     QPushButton *m_analyzeButton = nullptr;
+    bool m_buildBeforeAnalysis = true;
 };
 
 } // namespace Internal