tests: Enable some itemmodels tests that don't depend on Qt Widgets

Make qabstractproxymodel and qidentityproxymodel build and run
even if -no-widgets is used since they don't depend on Qt Widgets.

Change-Id: I48bc2f6a78812b1bf0083f76c6a4e106f4e38650
Reviewed-by: Stephen Kelly <stephen.kelly@kdab.com>
configure: Fix xkbcommon summary output

On systems where xkbcommon >= 0.2.0 the output should be

  xkbcommon .............. yes (system library)

instead of

  xkbcommon .............. yes

Change-Id: I5807946e61814d414a68a15ad96c91f25c9482ee
Reviewed-by: Gatis Paeglis <gatis.paeglis@digia.com>
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>