Don't just use an arbitrary toolchain, which might break esp. for Symbian.
Instead, retrieve the toolchain from the project, or in the case of the Qt Options
page let the user choose.

Change-Id: I6d271c485420e609d223d8cece754ef84e573745
Reviewed-on: http://codereview.qt.nokia.com/1978


Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Daniel Teske <daniel.teske@nokia.com>