cmd/compile: fix any in -G=0 mode

Fixes go test -gcflags=all=-G=0 -short std,
except for the packages with generics in their tests
(constraints, encoding/xml), and except for the
go/internal/gcimporter and go/types tests,
because the compiler does not preserve any
in its -G=0 export information.
(That's probably acceptable for now.)

Fixes cd test/; GO_BUILDER_NAME=longtest go run run.go
completely, which should fix the longtest builder.

Fixes #50159.

Change-Id: I9390972239c18831833edd6530191da2842b876b
Reviewed-on: https://go-review.googlesource.com/c/go/+/371715


Trust: Russ Cox <rsc@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>