Build system should support building using a device profile (mkspec) outside of the Qt source tree

Ideally it is possible to have a "device profile" outside of the Qt source tree eg:
configure -embedded arm -device <PATH TO DEVICE PROFILE>
such a device profile would include:

• the qmake.conf and related files to use
• any device specific plugins
• any data to install into the device's image ( eg /etc/pointercal)

At least
1) configure should support a -xplatform argument that is an absolute path
2) qmake can resolve in the custom qmake.conf includes of files in the source's mkspecs directory
include (mkspecs/wincewm60professional-msvc2008/qmake.conf)