Mozilla Pango vs Thai

I'm confused about current state of Pango vs Mozilla.
Reading a few bugzilla issues (#215219 and #214715) and
I still don't get the picture.

My understanding is that
- Mozilla 1.8 will use system Pango if enable Pango at compilation
- the old 'enable ctl' will not be used

I run the built
ftp://ftp.mozilla.org/pub/mozilla.org/mozilla/releases/mozilla1.7/contrib/mozilla-1.7-i686-pc-linux-gnu-gtk2-xft-pango.tar.gz
And it work for Thai.

How can I build 1.7.3 to work like this?
Which patch should I use?

Thanks.