illumos does not support latin1.  Use iso-8859-1 instead.

--- glib-2.82.0/gio/tests/converter-stream.c.orig
+++ glib-2.82.0/gio/tests/converter-stream.c
@@ -1174,7 +1174,7 @@
   gchar *to;
   gchar *from;
 
-  converter = (GConverter *)g_charset_converter_new ("utf-8", "latin1", &error);
+  converter = (GConverter *)g_charset_converter_new ("utf-8", "iso-8859-1", &error);
   g_assert_no_error (error);
   g_object_get (converter,
                 "to-charset", &to,
@@ -1182,7 +1182,7 @@
                 NULL);
 
   g_assert_cmpstr (to, ==, "utf-8");
-  g_assert_cmpstr (from, ==, "latin1");
+  g_assert_cmpstr (from, ==, "iso-8859-1");
 
   g_free (to);
   g_free (from);