Simply specify the import path you want to build, and xgo will do the rest:
xgo github.com/project-iris/iris
...
ls -al-rwxr-xr-x 1 root root 6776500 Nov 24 16:44 iris-darwin-386
-rwxr-xr-x 1 root root 8755532 Nov 24 16:44 iris-darwin-amd64
-rwxr-xr-x 1 root root 10135248 Nov 24 16:44 iris-linux-386
-rwxr-xr-x 1 root root 12598472 Nov 24 16:44 iris-linux-amd64
-rwxr-xr-x 1 root root 10040464 Nov 24 16:44 iris-linux-arm
-rwxr-xr-x 1 root root 7516368 Nov 24 16:44 iris-windows-386.exe
-rwxr-xr-x 1 root root 9549416 Nov 24 16:44 iris-windows-amd64.exe
If the path is not a canonical import path, but rather a local path (starts with
a dot . or a dash /), xgo will use the local GOPATH contents for the cross
compilation.