This gracefully disable ffmpeg, gstreamer, cups and cloudprint optional
dependencies when they are not available, while still giving full
control to distributors using -Dauto_features=enabled.
Use feature options for things that are optional features,
update the docs.
Visible changes here is that the 'print-backends' option
got renamed to 'print' to go better with 'media', and the
'tracker3' option got renamed to 'tracker'.
For options that have been changed into features, the
syntax now is -Dfeature=enabled or -Dfeature=disabled
or -Dfeature=auto.
Visual Studio does not allow decorating functions with '__declspec (dllexport)'
if a prototype exists and is not decorated with '__declspec (dllexport)' as
well, so we cannot just decorate g_io_module_[load|unload|query] in the various
module sources with G_MODULE_EXPORT because the prototypes of these functions
have been marked with _GLIB_EXTERN, which equates to 'extern' unless overridden
Fix this by overriding _GLIB_EXTERN with the appropriate visibility flag, as we
have used to define _GDK_EXTERN. Unfortunately, we can't just use _GDK_EXTERN
G_MODULE_EXPORT as they may have not been defined yet for our use
Do this across the board for all modules, even if they are not buildable on
Visual Studio nor Windows, for consistency's sake.
We were looking for the cups headers and the cups lib in the default locations
which for example breaks with OpenBSD where the cups headers are under /usr/local/include/
Instead just use the "cups" dependency type from meson which internally uses cups-config.
See #1967
Ported to master from !963
httpGetAuthString() was added with cups 1.3 and we depend on a newer version
now. The direct field access was a fallback in case httpGetAuthString()
was missing, so this can also be dropped.
Ported to master from !938
Instead of having separate options for each print backend, we can use
the same approach as the input method modules: a single option, with a
comma-separated list of print backends.
