I see now. 
This has two consequences:
- every time you run go, you must first ensure that /tmp/go is bound onto
  $GOROOT in the current process environment
- your /tmp had better not be too temporary (some people use ramfs to mount
  /tmp as an in-memory filesystem)
This was the issue. 

I re-ran those binds, and go projects work now. 

I will install it properly now