all.rc: make sure the Go tools end up in /bin

At least one test (in package runtime) depends
on `go' being in $path. We simply bind GOROOT/bin
before /bin to make sure the latest copy of the
binary is accessible there.

R=rsc, rminnich, ality
CC=golang-dev
https://codereview.appspot.com/7391047

Committer: Ron Minnich <rminnich@gmail.com>