ClangTools: Show hint when disabling "Build the project before analysis."

Show also the same hint as a tooltip.

Fixes: QTCREATORBUG-22382
Change-Id: If1b594994cea387d6727775ce4c28c21d51f2d86
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@qt.io>
Reviewed-by: David Schulz <david.schulz@qt.io>

src/plugins/clangtools/clangtoolsutils.h

@@ -41,5 +41,8 @@ namespace Internal {
 
 QString createFullLocationString(const Debugger::DiagnosticLocation &location);
 
+QString hintAboutBuildBeforeAnalysis();
+void showHintAboutBuildBeforeAnalysis();
+
 } // namespace Internal
 } // namespace ClangTools