When cross-compiling, we now create a target_qt.conf file that's to be
used with the host Qt's qmake. With "qmake -qtconf .../target_qt.conf"
projects can be cross-built against the cross-built Qt.
We also create wrapper scripts for the host qmake to save the user from
passing the -qtconf argument.
Fixes: QTBUG-82581
Change-Id: Ib5866e7e820369efea9eb3171e3e3e3ca5c0c3c1
Reviewed-by: Alexandru Croitor <alexandru.croitor@qt.io>