build: fix buildscript breakage after all.bash

Fix from Russ. Tested that multiple builds in a row
work again.

R=rsc, rsc
CC=golang-dev
https://golang.org/cl/5599047

src/buildscript.sh

@@ -35,6 +35,8 @@ set -e
 		s/\$WORK/"$WORK"/g
 		s;"\$GOBIN"/go;&_bootstrap;g
 		s;\\;/;g
+		s/go_bootstrap-tool/go-tool/g
+		s;"\$GOBIN"/go-tool;"$GOROOT"/bin/go-tool;g
 	'
 	)>$targ
 	chmod +x $targ