cmd/compile: prevent un-necessary wrapping in switch statement
Follow up discussion in CL 594575.
The wrapping in "any" is only necessary if either casType or tagType is
an interface, as "==" in this situation is implemented by upconverting
to an interface anyway.
Change-Id: I73da771d25685a23eec612ac696965c892db4764
Reviewed-on: https://go-review.googlesource.com/c/go/+/596555
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Dmitri Shuralyov <dmitshur@google.com> Reviewed-by: Keith Randall <khr@golang.org> Reviewed-by: Keith Randall <khr@google.com>