Configuring for X32 (not X86, not X64)?

[Jeffrey Walton]

We received a few bug reports from a Debian maintainer when he
testedus under X32 (related, see https://wiki.debian.org/X32Port). We
roughly know where the problems are, but Debian does not appear to
have a working GCD for X32 so we can't [easily] investigate most of
the issues further (related, see
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=799556).

I'm trying to build the latest GDB 7.10 from sources. When I
configure, it looks like the system is mis-detected:

    # cd gdb-7.10
    # ./configure --prefix=/usr/local
    checking build system type... x86_64-unknown-linux-gnu
    checking host system type... x86_64-unknown-linux-gnu
    checking target system type... x86_64-unknown-linux-gnu
    ...

Since I think the detection triplet should include something like
"linux-x32", I stopped it and tried:

    # export CFLAGS="-mx32"
    # export CXXFLAGS="-mx32"
    # ./configure --prefix=/usr/local
    checking build system type... x86_64-unknown-linux-gnu
    checking host system type... x86_64-unknown-linux-gnu
    checking target system type... x86_64-unknown-linux-gnu
    ...
    checking for makeinfo... no
    /root/gdb-7.10/missing: 81: /root/gdb-7.10/missing: makeinfo: not found
    checking for expect... no
    ...

I don't know of a way to get Autotools to list its triplets (related,
see http://gnu-autoconf.7623.n7.nabble.com/How-To-Configure-for-Android-Redux-for-x86-64-td19966.html),
so I'm not sure what else I can do to try and get things pointed in
the right direction.

I might be making an incorrect leap, so my first question is: does the
configuration appear to be correct?

If its not correct, then my second question is, how should I be configuring?