building a biarch x86_64/i686 toolchain

[tom fogal <tfogal@xxxxxxxxxxxxxxxxx>]

I've been reading around for a while now trying to figure out how to build
a biarch toolchain for use on my amd64 system. Currently everything on the
system is 32bit, including the kernel; the end goal is a compiler set that
will generate i686 compatible code when invoked as
'gcc -m32 file.c'
and x86_64 compatible/optimized code when invoked as
'gcc -m64 file.c' or 'gcc file.c'

this is a linux machine.