This reverts commit 1918c689d7.
The template gets always instantiated in QObjectPrivate::connect, even
if the connection types is not Qt::(Blocking)QueuedConnection. For
non-queued connections we however support using incomplete types in
connect. The only way to fix this would be to make the connection type a
template parameter of QObjectPrivate::connect (or at lesat pass some
compile time constant indicating "blocking"-ness) along, so that we can
use if constexpr instead of if. As all involved classes are private, we
can postpone investigating this solution to 6.1
Change-Id: Ieffaf015f8e60ca6ac6f85eb9e2756e480060b4f
Reviewed-by: Lars Knoll <lars.knoll@qt.io>
331a200b97