build: create bin and pkg directories as needed; drop from hg

R=dsymonds, r
CC=golang-dev
https://golang.org/cl/2050043

bin/~place-holder~

-Command binaries are installed in this directory.
-
-Mercurial does not maintain empty directories.
-This file helps.

pkg/~place-holder~

-Package binaries are installed in this directory tree.
-
-Mercurial does not maintain empty directories.
-This file helps.

src/env.bash

@@ -22,7 +22,7 @@ if [ "$DIR1" != "$DIR2" ]; then
 fi
 
 export GOBIN=${GOBIN:-"$GOROOT/bin"}
-if [ ! -d "$GOBIN" ]; then
+if [ ! -d "$GOBIN" -a "$GOBIN" != "$GOROOT/bin" ]; then
 	echo '$GOBIN is not a directory or does not exist' 1>&2
 	echo 'create it or set $GOBIN differently' 1>&2
 	exit 1

src/make.bash

@@ -10,6 +10,12 @@ if [ ! -f env.bash ]; then
 fi
 . ./env.bash
 
+# Create target directories
+if [ "$GOBIN" = "$GOROOT/bin" ]; then
+	mkdir -p "$GOROOT/bin"
+fi
+mkdir -p "$GOROOT/pkg"
+
 GOROOT_FINAL=${GOROOT_FINAL:-$GOROOT}
 
 MAKEFLAGS=${MAKEFLAGS:-"-j4"}