cmd/compile: NewSelectorExpr use n.Pos instead of base.Pos
cmd/compile: NewSelectorExpr use n.Pos instead of base.Pos

Fixes #49436

Change-Id: I4c8851e7aaee631d5eb22f2ef0aea5a25e936d87
Reviewed-on: https://go-review.googlesource.com/c/go/+/361917
Run-TryBot: Dan Scales <7338a4f274e3bf1354488b9d1f344f4c9a69a8fb@google.com>
TryBot-Result: Go Bot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Keith Randall <8c99c3a9284e493be632950b84cd789d08ed3e9d@golang.org>
Trust: David Chase <ae171625adc8645b8b79b7e405a6da5aba5341e0@google.com>

cloudflare/go,cloudflare/go,golang/go,cloudflare/go,golang/go,CAFxX/go,CAFxX/go,CAFxX/go,golang/go,nawawi/go,nawawi/go,CAFxX/go,golang/go,cloudflare/go,nawawi/go,CAFxX/go,CAFxX/go,nawawi/go,golang/go,cloudflare/go,nawawi/go,cloudflare/go,nawawi/go,cloudflare/go,golang/go,CAFxX/go,nawawi/go,nawawi/go,CAFxX/go,cloudflare/go,golang/go,golang/go