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://golang.org/cl/7391047

src/all.rc

@@ -9,5 +9,6 @@ if(! test -f make.rc){
 }
 
 . ./make.rc --no-banner
+bind -b $GOROOT/bin /bin
 ./run.rc --no-rebuild
 $GOTOOLDIR/dist banner  # print build info