use auto-defined QT_BUILD_*_LIB variables
use auto-defined QT_BUILD_*_LIB variables

Change-Id: I6bafddeb11e764d17c5e9d9147c4e60da59c80a7
Reviewed-by: Andrew Stanley-Jones <3158427ccc6af852b3b80aff3045d95d14f60128@nokia.com>

qtproject/qtsystems,qtproject/qtsystems