[tex-live] [nodblaccnt]{t5} workaround?

[Vasile Gaburici]

I wrote a script which produces (amongst other more useful things)
test pages from Dominique's config/ucf files. I'm having trouble with
the Vietnamese encoding though. In the latin-b.ucf file there's a
section:
{
FONTENC T5
PACKAGE [nodblaccnt]{t5}
U+01A0  \horn O                 # [Ơ]
U+01A1  \horn o                 # [ơ]
}
But I can't find the t5 package in the current vntex package, and I
cannot find the nodblaccnt option mentioned in any of vntex's files
either. Pdflatex dies with:

! LaTeX Error: Command \horn{O} unavailable in encoding T5.

See the LaTeX manual or LaTeX Companion for explanation.
Type  H <return>  for immediate help.
 ...

l.46 \unichar{"01A0}
                     % \horn O