GCC: Actually use sysroot for header path detection

Function signature was prepared for that on
4c6b794774 but it wasn't really used

Change-Id: I1ee7059a00f0441d42a117b8f8d2c8c776d93815
Reviewed-by: Tobias Hunger <tobias.hunger@nokia.com>
Reviewed-by: Daniel Teske <daniel.teske@nokia.com>

src/plugins/qt4projectmanager/qt4project.cpp

@@ -527,7 +527,7 @@ void Qt4Project::updateCppCodeModel()
 
         QList<HeaderPath> headers;
         if (tc)
-            headers = tc->systemHeaderPaths(); // todo pass cxxflags?
+            headers = tc->systemHeaderPaths(SysRootKitInformation::sysRoot(k)); // todo pass cxxflags?
         if (qtVersion) {
             headers.append(qtVersion->systemHeaderPathes(k));
         }