Set variable to force RVCT version for Symbian

Set the variable to force the RVCT version when building for
Symbian using SBSv2. This is currently hardcoded to version 2.2
since we do not yet support RVCT 4.

src/plugins/qt4projectmanager/qt-s60/rvcttoolchain.cpp

@@ -261,6 +261,8 @@ void RVCTToolChain::addToEnvironment(ProjectExplorer::Environment &env)
         m_mixin.addEpocToEnvironment(&env);
         break;
     }
+    // we currently support RVCT v2.2 only:
+    env.set(QLatin1String("QT_RVCT_VERSION"), QLatin1String("2.2"));
 }
 
 QString RVCTToolChain::makeCommand() const