[dev.regabi] cmd/compile: replace ir.Name map with ir.NameSet for SSA 2
[dev.regabi] cmd/compile: replace ir.Name map with ir.NameSet for SSA 2

Same as CL 284897, the last one.

Passes toolstash -cmp.

Updates #43819

Change-Id: I0bd8958b3717fb58a5a6576f1819a85f33b76e2d
Reviewed-on: https://go-review.googlesource.com/c/go/+/285913
Run-TryBot: Baokun Lee <b86f6db284d374188d561d46b45b188d5631609a@golangcn.org>
TryBot-Result: Go Bot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Matthew Dempsky <e56ac2c500064424afac424d4b5e53bd0570a731@google.com>
Trust: Baokun Lee <b86f6db284d374188d561d46b45b188d5631609a@golangcn.org>

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