Make qtcreatorlibrary.pri work for 3rd party libraries

Please make qtcreatorlibrary.pri to work correctly with libraries outside Qt Creator source tree like qtcreatorplugin.pri works correctly for plugins outside Qt Creator source tree. Now have link errors using it under Linux, Mac or Windows. Forced to write own qtc_pluginlibrary.pri instead of standard to make it work.

Plugin example: https://github.com/akontsevich/ConnectedCreatorPlugin

Library: https://github.com/akontsevich/ConnectedCreatorPlugin/tree/master/lib/qtelemetry

Thanks!