Make variable manager static.

This makes it follow our preferred singleton pattern.

Change-Id: I230e5ac5ef7f156da7123f7efe3a49bcb6a20669
Reviewed-by: hjk <hjk121@nokiamail.com>

src/plugins/projectexplorer/buildconfiguration.cpp

@@ -73,7 +73,7 @@ bool BuildConfigMacroExpander::resolveMacro(const QString &name, QString *ret)
         *ret = QDir::toNativeSeparators(m_bc->buildDirectory());
         return true;
     }
-    *ret = Core::VariableManager::instance()->value(name.toUtf8());
+    *ret = Core::VariableManager::value(name.toUtf8());
     return !ret->isEmpty();
 }
 } // namespace Internal