C++: export the SymbolSearcher to use it outside CppTools.

Change-Id: If60f3c1800a678f6e3b49eb9d78eab9b2d323fb3
Reviewed-by: Erik Verbruggen <erik.verbruggen@digia.com>

src/plugins/cpptools/cppindexingsupport.h

@@ -40,7 +40,7 @@
 
 namespace CppTools {
 
-class SymbolSearcher: public QObject
+class CPPTOOLS_EXPORT SymbolSearcher: public QObject
 {
     Q_OBJECT