Add ability to pass GOOS and GOARCH as build parameters

[nimeshnsat]

Enable make.go to accept GOOS and GOARCH as external parameters so that silver binaries for different platforms can be built from a single checkout. This PR doesn't break the existing parameter interface (where it accept a single non flagged optional parameter call 'action')

ex: go run make.go --goos=darwin --goarch=amd64 all