Building FreeBSD for two or more architectures but not all

[Thomas Mueller]

How would I build FreeBSD, in this case 9.0-RELEASE, for two or more architectures, in this case i386 and amd64?

One build (amd64) would update the present system (9.0 RC3), but the other would go on a USB stick, likely 16 GB.

Real question is how to keep things like /usr/obj and other things from the two builds separate.

I don't want to 'make universe' when I won't run on anything other than i386 and amd64.

I want to build both on the new computer because the old computer is short on disk space and has only 256 MB RAM.

Tom