GLib conversion failure on OpenBSD when building gtk2

[Alexander Nasonov <alnsn%yandex.ru@localhost>]

I cannot compile x11/gtk2 on OpenBSD 4.1 because an execution of 
gtk-update-icon-cache --force <more args> fails with "GLib: Cannot convert 
message: Conversion from character set 'UTF-8' to '646' is not supported" 
message (it fails even without <more args> if executed manually).
I found that glib2 function _g_locale_charset_raw calls nl_langinfo (CODESET) 
which returns "646".
Code around nl_langinfo call looks like

# if HAVE_LANGINFO_CODESET

  /* Most systems support nl_langinfo (CODESET) nowadays.  */
  codeset = nl_langinfo (CODESET);

# else

  /* On old systems which lack it, use setlocale or getenv.  */
  ...

I disabled the first branch and ran LANG=en_US.ISO8859-1 gtk-update-icon-cache 
--force manually. It executed without an error but it still fails if I run 
LANG=en_US.ISO8859-1 bmake.
Presumably, pkgsrc either clean LANG or set it to a portable value (which is 
good) but it makes me wonder how to patch the _g_locale_charset_raw function 
without hardcoding "en_US.ISO8859-1" into it.

BTW,
cvs comment of the last version of nl_langinfo.c says that

> CODESET support. okay millert@, otto@
> 
> (not really useful for now, it mostly helps some programs which want
> to use it, it will become useful when we have full 16 bits locale).

http://www.openbsd.org/cgi-bin/cvsweb/src/lib/libc/locale/nl_langinfo.c

Does anybody has an idea how to fix this problem?
-- 
Alexander Nasonov