Fix include path order in C++ dependency scanner
Fix include path order in C++ dependency scanner

The list of include paths must not be stored in a temporary
set. Otherwise the order of include paths is undefined.
Also, since introduction of merged top-level modules in commit 16404c35
we don't need to recurse through the dependency hierarchy.

Change-Id: I50a843fc85dbf1cb04883774d43e5904da815579
Reviewed-by: Christian Kandeler <3aa99dcdd3f0cac61fb81c2a11771c0cc2497607@qt.io>

qtproject/qt-labs-qbs,qt-labs/qbs,qt-labs/qbs,qt-labs/qbs,qt-labs/qbs,qt-labs/qbs,qtproject/qt-labs-qbs,qtproject/qt-labs-qbs,qt-labs/qbs,qtproject/qt-labs-qbs,qtproject/qt-labs-qbs,qtproject/qt-labs-qbs,qt-labs/qbs,qtproject/qt-labs-qbs