Add support for building i386 releases/packages on amd64

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As it stands now, it is not possible to build i386 releases or packages on 
amd64 farbot build 
servers without some tweaking. When using binary releases packages cannot be 
built unless 
ARCH i386 is set in the release's PackageBuildOptions, and this should be 
automatic. 
Furthermore it is necessary to symlink /libexec/ld-elf.so to 
/libexec/ld-elf32.so in the package 
build chroot before farbot chroots there and starts building packages. An 
option should be 
added to the farbot.conf file to just specify that the architecture of the 
release is something other 
than what the build server runs to make this happen automatically.

I've not yet tested cross-building a release from source using a different 
architecture, but I 
suspect that TARGET and TARGET_ARCH will need to be set to i386 for building 
the kernel and 
world.

Cross compiling for other architectures would be cool, but supporting that I'm 
sure will be 
harder if possible at all. Plus I don't have any non-i386/amd64 hardware to 
test with. For now 
let's try just being able to build i386 on amd64.

Original issue reported on code.google.com by [email protected] on 13 Aug 2008 at 1:14