What steps will reproduce the problem?

Cross compiling from amd64 -> 386 on a darwin/amd64 10.7.4 machine produces 

odessa(~/go/src) % GOARCH=386 ./make.bash 2>&1 | tail
os/user
testing
testing/iotest
testing/quick
# cmd/go
/Users/dfc/go/pkg/darwin_386/crypto/x509.a(_all.o): malformed mach-o file: unsupported
scattered relocation 2/1
/Users/dfc/go/pkg/darwin_386/runtime/cgo.a(_all.o): malformed mach-o file: unsupported
scattered relocation 2/1
# cmd/godoc
/Users/dfc/go/pkg/darwin_386/crypto/x509.a(_all.o): malformed mach-o file: unsupported
scattered relocation 2/1
/Users/dfc/go/pkg/darwin_386/runtime/cgo.a(_all.o): malformed mach-o file: unsupported
scattered relocation 2/1

Please use labels and text to provide additional information.

% xcodebuild -version
Xcode 4.2.1
Build version 4D502

% uname -a
Darwin odessa.fritz.box 11.4.0 Darwin Kernel Version 11.4.0: Mon Apr  9 19:32:15 PDT
2012; root:xnu-1699.26.8~1/RELEASE_X86_64 x86_64

yes, the command line tools are installed, in this version of Xcode they are not an
optional extra.