fix order of libraries in gcc link command line

Array.uniqueConcat cannot be used to remove duplicates, because the
right-most duplicates are removed. To keep the dependencies ordered
correctly, we must remove the left-most duplicates instead.

Task-number: QBS-503
Change-Id: I5a2834905f650e0921bc42f9cffe15b71128ff7e
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>
Reviewed-by: Christian Kandeler <christian.kandeler@digia.com>
make keyFromElem(ArtifactProperties) unambiguous

Change-Id: I4e84dbe487364f73a5d523af778689e7fe2086f4
Reviewed-by: Christian Kandeler <christian.kandeler@digia.com>
make Rule.toString unambiguous

Change-Id: I36afb8545c93737bcd62513d87d8325a399b7e6b
Reviewed-by: Christian Kandeler <christian.kandeler@digia.com>