Fix "gvm cross" for Go 1.4

> go tool dist: opendir /home/user/.gvm/gos/go1.4/src/pkg/runtime: No such file or directory
> ERROR: Couldn't compile runtime library for darwin amd64

I also took the liberty of including a second commit which fixes some whitespace inconsistencies in the same file (but I'm happy to remove/separate that commit if preferred).
I can't help but think that it might be more accurate here to look for `"$GOROOT/pkg/${GOOS}_${GOARCH}/runtime.a"` or similar, but I haven't done the necessary testing to verify that this would work across a reasonable number of Go versions (but it would catch attempted installs better, and make them easier to repeat).

It'd obviously need to come with the same logic above in `display_list`, so that's a project for a separate PR, IMO. :)