It doesn't make much sense to look for X11 related packages on
macOS and Windows by default. Usually they would not be there, and
as a result the configuration step would show a long list of scary
not found packages, and also eat precious configure time.
Change the conversion script to allow putting conditions around
generated find_package calls.
These conditions can be manually set in the conversion script
library mapping, using the emit_if argument,
which we do for the X11 and Wayland related packages.
They are also computed by checking which features use a given library,
and if the feature is protected by a simple emitIf condition like
config.linux, the relevant library find_package call will be protected
by the same condition.
If a developer still wishes to look for all packages, they can define
the CACHE variable QT_FIND_ALL_PACKAGES_ALWAYS to ON.
The relevant configure.cmake files are regenerated in this patch.
Change-Id: I6f918a94f50257ec41d6216305dae9774933389a
Reviewed-by: Tobias Hunger <tobias.hunger@qt.io>
e4b8c488bd