Fix broken links in Qt modules documentation.

Change-Id: I57fbbd66e500a8172346acf45f84350c7ebb394c
Reviewed-by: Jake Petroules <jake.petroules@petroules.com>
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@digia.com>
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>
do not collect cpp.platformDefines from dependent modules

cpp.platformDefines is dependent on properties that are set in the
product's or a group's instance of cpp. Therefore we must not combine
the values of this property from the input and its dependencies.

Task-number: QBS-433
Change-Id: Id90ffc9d8193d8425e62ffc3d0b1d3cca83f8dff
Reviewed-by: Christian Kandeler <christian.kandeler@digia.com>