b785d4813e introduced breakage in Qt
modules for 5.6 and 5.9, especially visible is Qt Webkit.
This was manifested by having a non-sensical build log where it is using
the top-level `src` attribute as source instead of Qt Webkit's own
source.
Were it not for the `src` top-level attribute (which is a legit
package), the error would have been made obvious by passing `null` to
`src`.
This partily reverts newly introduced way `src` can be passed to a
qtModule, instead relying on extending the `srcs` attrset.
For ZHF #45960
This is the first time since 5.9 that we also update `qtwebkit`.
`qtwebkit` is not maintained by Qt anymore and thus, we switch to the
community port as for example arch has done. To prevent pulling in
single patches, we just stick to the latest git version.
