Use new configure system for all package detection.
Move config test execution to new configure system.
However, keep old configure.prf for error hanlding.
Split configuration summary into:
 * optional system libraries used
 * required system libraries
 * required system libraries for qpa-xcb (on linux)

Change-Id: I5108456caa024a1ada9bb54750693064a2d36f78
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>