BuildSystem: Fix move semantics of ParseGuard and related code

This avoids a spurious set of parsing started/finished signals.

Change-Id: I0c723f2a2ad679a5f6cffddf9f542ebc02192be8
Reviewed-by: Cristian Adam <cristian.adam@qt.io>
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

src/plugins/cmakeprojectmanager/cmakebuildsystem.cpp

@@ -114,6 +114,7 @@ CMakeBuildSystem::~CMakeBuildSystem()
 
 bool CMakeBuildSystem::validateParsingContext(const ParsingContext &ctx)
 {
+    QTC_ASSERT(!m_currentContext.guard.guardsProject(), return false);
     return ctx.project && qobject_cast<CMakeBuildConfiguration *>(ctx.buildConfiguration);
 }