GenericProject: Make dependency on CppTools optional

Especially in the light of the language server, the generic project is
currently the project one can use for language servers that require a
"project workspace".

Makes it possibly to run Qt Creator with
"-noload CppTools" if you still want to use generic
projects with some other language.

Change-Id: Ib9059289a2db4c44c0c1060a02fcdafacb885fbd
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@qt.io>

src/plugins/genericprojectmanager/genericproject.h

@@ -29,7 +29,9 @@
 #include <projectexplorer/project.h>
 #include <utils/fileutils.h>
 
-namespace CppTools { class CppProjectUpdater; }
+namespace CppTools {
+class CppProjectUpdaterInterface;
+}
 namespace Utils { class FileSystemWatcher; }
 
 namespace GenericProjectManager {
@@ -87,7 +89,7 @@ private:
     QStringList m_cxxflags;
     QStringList m_cflags;
 
-    CppTools::CppProjectUpdater *m_cppCodeModelUpdater = nullptr;
+    CppTools::CppProjectUpdaterInterface *m_cppCodeModelUpdater = nullptr;
 
     Utils::FileSystemWatcher * const m_deployFileWatcher = nullptr;
 };