cmd/compile: fix ir.StaticValue for ORANGE

cmd/compile: fix ir.StaticValue for ORANGE

Range statement will mutate the key and value, so we should treat them as reassigned.

Fixes #59572

Change-Id: I9c6b67d938760a0c6a1d9739f2737c67af4a3a10
Reviewed-on: https://go-review.googlesource.com/c/go/+/483855
Run-TryBot: Wayne Zuo <wdvxdr@golangcn.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Auto-Submit: Keith Randall <khr@golang.org>
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Keith Randall <khr@golang.org>