buildscripts: move to buildscript directory

        Fixes #2717.

R=r, rsc, dsymonds
CC=golang-dev
https://golang.org/cl/5545069

src/buildscript.sh

@@ -9,7 +9,7 @@ for sys in $GOOSARCHES
 do
 	export GOOS=$(echo $sys | sed 's/_.*//')
 	export GOARCH=$(echo $sys | sed 's/.*_//')
-	targ=buildscript_${GOOS}_$GOARCH.sh
+	targ=buildscript/${GOOS}_$GOARCH.sh
 	rm -f $targ
 
 	(echo '#!/usr/bin/env bash

src/make.bash

@@ -93,7 +93,7 @@ echo; echo; echo %%%% making runtime generated files %%%%; echo
 if $USE_GO_TOOL; then
 	echo
 	echo '# Building go command from bootstrap script.'
-	./buildscript_${GOOS}_$GOARCH.sh
+	./buildscript/${GOOS}_$GOARCH.sh
 
 	echo '# Building Go code.'
 	go install -a -v std