This check serves only to provide a more descriptive error if the output
directory doesn't exist. That isn't useless, but I don't see why this tool
specifically should do this when no other part of the toolchain does.
For #58102.
Change-Id: I01cf9db2cc1dad85c3afd8a6b008c53f26cb877a
Reviewed-on: https://go-review.googlesource.com/c/go/+/569336 Reviewed-by: Cherry Mui <cherryyz@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>