dbus1_linked is only evaluated to true when the dbus package is found.
If it was not found, then it makes no sense to link against the
_nolink target, because no package was found in the first place.
When the package is not found, QtDBus uses a minimal dbus header which
is included with QtDBus sources, so there is no need for the _nolink
target.
This amends cc141cc5c6 and fixes a build
failure on macOS.
Change-Id: I71dcbb7465ad13b0bf03579f51412c373125caba
Reviewed-by: Tobias Hunger <tobias.hunger@qt.io>