According to gtk+ changelog GtkFileSystem is now a private class, useful only at debugging.

Anyways during compile i got this:

In file included from gtkfilechooserutils.h:25,
                 from gtkfilechooserutils.c:27:
gtkfilechooserprivate.h:24:31: error: gtk/gtkfilesystem.h: No such file or directory
In file included from gtkfilechooserutils.h:25,
                 from gtkfilechooserutils.c:27:
gtkfilechooserprivate.h:39: error: expected ';', ',' or ')' before '*' token
gtkfilechooserprivate.h:41: error: expected ';' before 'GtkFilePath'
gtkfilechooserprivate.h:76: error: expected '=', ',', ';', 'asm' or '__attribute__' before '*' token
gtkfilechooserprivate.h:78: error: expected ';', ',' or ')' before '*' token

etc. etc. et.