Don't use "-linkobj" when compile for a binary or test

[sluongng]

Currently in compilepkg.go, when we invoke go tool compile, we are unconditionally adding -linkobj to create 2 separate artifacts: .x for downstream library compilation and .a for downstream binary linking.

This is efficient for go_library, but for the compilation which happens under go_test and go_binary, the output artifact(s) will not be used for any other downstream actions except GoLink for that test/binary to create the final Go executable.

So for the GoCompilePkg action under go_test and go_binary, it will be better if we remove -linkobj and only generate the .a file. In other words, we should only be using -linkobj when the downstream consumer of the artifact is unclear, such as for the GoCompilePkg action under go_library or go_proto_library.