Map the dlopen feature to 'ON'. The effect is that cmake will figure
out whether or not linking to 'dl' is necessary or not.
The user-visible feature is 'library' anyway: That enables dynamic
library loading -- and will link in 'dl' as needed.
Change-Id: I0d68275a7234efba7f926150f120bb37b4a1163f
Reviewed-by: Albert Astals Cid <albert.astals.cid@kdab.com>
Reviewed-by: Frederik Gladhorn <frederik.gladhorn@qt.io>