devel/rubygem-glib2: unbreak with glib 2.76

rbglib_bookmarkfile.c:39:1: error: static declaration of 'g_bookmark_file_get_type' follows non-static declaration
g_bookmark_file_get_type(void)
^
/usr/local/include/glib-2.0/gobject/glib-types.h:402:9: note: previous declaration is here
GType g_bookmark_file_get_type (void) G_GNUC_CONST;

^

rbglib_bookmarkfile.c:50:9: warning: 'G_TYPE_BOOKMARK_FILE' macro redefined [-Wmacro-redefined]
#define G_TYPE_BOOKMARK_FILE (g_bookmark_file_get_type())

^

/usr/local/include/glib-2.0/gobject/glib-types.h:337:9: note: previous definition is here
#define G_TYPE_BOOKMARK_FILE (g_bookmark_file_get_type ())

^

PR: 270087
Reported by: antoine (via exp-run)