gofmt-runner executes the real gofmt based on the GOROOT of the
default Go compiler.
The intent is to make switching between Go SDKs using
https://godoc.org/golang.org/dl easier, mostly by avoiding dangling
gofmt symlinks to a removed SDK.
If you use golang.org/dl, you end up with multiple goX.Y
executables. To choose which one is the default Go version to run, the
easiest thing is to symlink one of them to go. The easiest way to
choose a gofmt version has been to make gofmt be a symlink
pointing to something like /home/MYUSER/sdk/go1.11.2/bin/gofmt.
That's just annoying, and prone to dangling symlinks as you remove old
Go versions from ~/sdk.
Instead, make your gofmt executable be gofmt-runner, and it'll use
your default go command to find out which gofmt version to
execute. From now on, as you upgrade Go versions, you only need to
update the go symlink.