Problem: You’re on a i386 machine, and you need to build for amd64, or vice-versa. Solution:

Get the libc for the other architecture. Get both, one of which you’ll already have:

# Debian / Ubuntu family
sudo apt-get install libc6-dev-amd64 libc6-dev-i386

Build the Go compiler for the other architecture:

cd $GOROOT/src
GOARCH=amd64 ./make.bash    # or GOARCH=386 for the other direction

Set the architecture before building your program:

GOARCH=amd64 go install <my_project>  # or GOARCH=386

The first two steps you only need to do once.

Thank you zephyrtronium in freenode#go-nuts for the help.

For other architectures, see Dave Cheney’s An introduction to cross compilation with Go