CppTools: Use a shared thread pool

Without this, too many threads are spawned, and loading a project takes
forever.

Change-Id: I3c22557ddd7bfb0c70f7b089c276432e3b003097
Reviewed-by: Eike Ziller <eike.ziller@theqtcompany.com>

src/plugins/cpptools/cppmodelmanager.cpp

@@ -58,6 +58,7 @@
 #include <QDir>
 #include <QMutexLocker>
 #include <QTextBlock>
+#include <QThreadPool>
 #include <QTimer>
 
 #if defined(QTCREATOR_WITH_DUMP_AST) && defined(Q_CC_GNU)
@@ -157,6 +158,7 @@ public:
     CppFindReferences *m_findReferences;
 
     SymbolFinder m_symbolFinder;
+    QThreadPool m_threadPool;
 
     bool m_enableGC;
     QTimer m_delayedGcTimer;
@@ -1196,4 +1198,9 @@ SymbolFinder *CppModelManager::symbolFinder()
     return &d->m_symbolFinder;
 }
 
+QThreadPool *CppModelManager::sharedThreadPool()
+{
+    return &d->m_threadPool;
+}
+
 } // namespace CppTools