Fix handling of weak frameworks with path names.

Previously if a path to a framework to be weakly linked was given (as
opposed to a framework name), it was strongly linked. The correct flag
to mark the library path as weakly linked is now applied.

Change-Id: I523fd84ba0967e68906611b32305aaf371b1a6b4
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>