dashboard: default to new compilers for windows amd64/386 builders

Revamp the setup for windows-amd64 and windows-386 builders so that we
default to using newer C compilers for Go 1.20 and main branch, but
older compilers for release branches (1.19 and prior). Instead of
having a series of "newcc" canary builders for windows, we now have a
series of "oldcc" builders for release branch use.

Note for posterity: we can prune these changes out in a couple of Go
release (once Go 1.20 becomes the oldest release we're testing).

Updates golang/go#35006.

Change-Id: I329b59a5d67c2c1ae65a30564a1c6a081b2523fa
Reviewed-on: https://go-review.googlesource.com/c/build/+/453095
Reviewed-by: Heschi Kreinick <heschi@google.com>
Run-TryBot: Than McIntosh <thanm@google.com>
Reviewed-by: Carlos Amedee <carlos@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>