Set Qt::AA_DontCreateNativeWidgetSiblings on Windows/Mac.
Set Qt::AA_DontCreateNativeWidgetSiblings on Windows/Mac.

Prevent creation of native windows for subwidgets, caused
by the welcome screen.

Task-number: QTCREATORBUG-10251

Change-Id: I2b475e963c5dfd1485f0876817c88d80fc2abd25
Reviewed-by: Eike Ziller <c142da16c73a95a82d35191bcc55b22835617128@digia.com>
Reviewed-by: Thomas Hartmann <588ee739c05aab7547907becfd1420d2b7316069@digia.com>

farseerri/git_code,amyvmiwei/qt-creator,amyvmiwei/qt-creator,darksylinc/qt-creator,xianian/qt-creator,darksylinc/qt-creator,farseerri/git_code,richardmg/qtcreator,richardmg/qtcreator,maui-packages/qt-creator,Distrotech/qtcreator,kuba1/qtcreator,maui-packages/qt-creator,AltarBeastiful/qt-creator,kuba1/qtcreator,farseerri/git_code,danimo/qt-creator,danimo/qt-creator,kuba1/qtcreator,richardmg/qtcreator,danimo/qt-creator,darksylinc/qt-creator,colede/qtcreator,amyvmiwei/qt-creator,martyone/sailfish-qtcreator,martyone/sailfish-qtcreator,kuba1/qtcreator,danimo/qt-creator,maui-packages/qt-creator,kuba1/qtcreator,colede/qtcreator,farseerri/git_code,martyone/sailfish-qtcreator,xianian/qt-creator,danimo/qt-creator,martyone/sailfish-qtcreator,kuba1/qtcreator,amyvmiwei/qt-creator,danimo/qt-creator,Distrotech/qtcreator,richardmg/qtcreator,kuba1/qtcreator,farseerri/git_code,Distrotech/qtcreator,farseerri/git_code,kuba1/qtcreator,darksylinc/qt-creator,AltarBeastiful/qt-creator,AltarBeastiful/qt-creator,maui-packages/qt-creator,Distrotech/qtcreator,kuba1/qtcreator,omniacreator/qtcreator,maui-packages/qt-creator,AltarBeastiful/qt-creator,colede/qtcreator,darksylinc/qt-creator,amyvmiwei/qt-creator,xianian/qt-creator,colede/qtcreator,martyone/sailfish-qtcreator,martyone/sailfish-qtcreator,omniacreator/qtcreator,xianian/qt-creator,richardmg/qtcreator,omniacreator/qtcreator,Distrotech/qtcreator,danimo/qt-creator,colede/qtcreator,amyvmiwei/qt-creator,xianian/qt-creator,darksylinc/qt-creator,martyone/sailfish-qtcreator,colede/qtcreator,richardmg/qtcreator,martyone/sailfish-qtcreator,AltarBeastiful/qt-creator,xianian/qt-creator,farseerri/git_code,darksylinc/qt-creator,omniacreator/qtcreator,maui-packages/qt-creator,farseerri/git_code,maui-packages/qt-creator,Distrotech/qtcreator,danimo/qt-creator,Distrotech/qtcreator,colede/qtcreator,danimo/qt-creator,AltarBeastiful/qt-creator,darksylinc/qt-creator,omniacreator/qtcreator,omniacreator/qtcreator,amyvmiwei/qt-creator,xianian/qt-creator,xianian/qt-creator,AltarBeastiful/qt-creator,richardmg/qtcreator,AltarBeastiful/qt-creator,martyone/sailfish-qtcreator,amyvmiwei/qt-creator,xianian/qt-creator,omniacreator/qtcreator