cmd/go: install -a fails if GOROOT is not writeable

[4a6f656c]

Currently 'go install -a' fails when run for packages under GOPATH, if the GOROOT is not
writeable:

$ sudo tar -C /usr/local -xzf go1.0.3.linux-amd64.tar.gz
$ echo $GOPATH
/home/jsing/src/mygo
$ go install -a example
go install runtime: open /usr/local/go/pkg/linux_amd64/runtime.a: permission denied

Obviously '-a' means all, however it would be useful if we could force a rebuild for all
of the dependencies under the GOPATH only (or skip dependencies in GOROOT).

[adg]

Comment 1:

I think this should wait until after Go 1.1.

Labels changed: added priority-later, removed priority-triage.

[rsc]

Comment 2:

I don't want to make the pattern language more complex. You can already do
cd $GOPATH
go install ./...

Status changed to WorkingAsIntended.