Avoid errors like

compiler/qv4ssa.cpp:660:59: error: no matching function for call to
'sort(QVector<QV4::IR::BasicBlock*>::iterator, QVector<QV4::IR::BasicBlock*>::iterator,
(anonymous namespace)::DominatorTree::calculateDFNodeIterOrder() const::Cmp)'

Change-Id: I4189bd621f1cef5e00b06f5b6b6dd430fefe653f
Reviewed-by: Erik Verbruggen <erik.verbruggen@digia.com>