These are here to prevent linker errors, since `gcontenttype.[ch]`
aren’t compiled on Windows or macOS.
The implementations are stubs to be filled out by someone who knows each
platform, at some point in the future.
Signed-off-by: Philip Withnall <withnall@endlessm.com>
Fixes: #1791
This is a hack for GLocalFileInfo to correctly get icons for directories.
Without this change content type for any W32 directory is NULL
(because there's no registry entry for "inode/directory" by default,
and in any way there's no file extension that means "directory" to put there),
and GLocalFileInfo uses content type to grab icons.
https://bugzilla.gnome.org/show_bug.cgi?id=748727
The code here was returning gtk-directory and similar names as
fallback, with a comment claiming that these are 'builtin gtk'.
But they aren't, anymore, so just return the standard names.
