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.
At least from GTK v3.22.30, the code disallows attempts to print PDF and
PS files using the LPR backend. Although it is not easy or possible for
GTK to determine if the printer can print these formats by querying lpr,
the print backend should allow lpr to try.
There are two uses cases:
- A filter is being used by lpr, specified in the printcap file, to process the
files prior to printing them.
- The printer can print PDF and PS files directly. There are many printers that
can print these formats, so GTK should allow for the possibility.
