[dev.regabi] cmd/compile: replace ir.Name map with ir.NameSet for dwarf

[dev.regabi] cmd/compile: replace ir.Name map with ir.NameSet for dwarf

Same as CL 284897, but for dwarf.

Passes toolstash -cmp.

Fixes #43819

Change-Id: Icbe43aa2e3cb96e6a6c318523c643247da8e4c74
Reviewed-on: https://go-review.googlesource.com/c/go/+/284899
Run-TryBot: Baokun Lee <bk@golangcn.org>
Trust: Baokun Lee <bk@golangcn.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>