cmd/compile: use exact constant in go_asm.h

cmd/compile: use exact constant in go_asm.h

Fixes #50523

Change-Id: Idab1b44d106250e9301d90ee6571f0ea51242dd9
Reviewed-on: https://go-review.googlesource.com/c/go/+/377074
Trust: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Liz Fong-Jones <lizf@honeycomb.io>
Reviewed-by: Emmanuel Odeke <emmanuel@orijtech.com>
Trust: Emmanuel Odeke <emmanuel@orijtech.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>