dispose of QMAKE_LIBDIR_FLAGS, "demote" QMAKE_FRAMEWORKPATH_FLAGS

dispose of QMAKE_LIBDIR_FLAGS, "demote" QMAKE_FRAMEWORKPATH_FLAGS

merge their content as early as possible into QMAKE_LIBS. that's where
they ultimately end up anyway, and this approach is way simpler.
QMAKE_FRAMEWORKPATH_FLAGS is also used for the compiler flags, so it
remains as such in this second function.

Change-Id: Idc3ba4a9b2569fce3252d5f5ddc3f6ebf93650cf
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@nokia.com>
Reviewed-by: Joerg Bornemann <joerg.bornemann@nokia.com>