cmd/compile: coalesce a few shift rules for wasm
cmd/compile: coalesce a few shift rules for wasm

Change-Id: I1b76daba90afd474390db8d9c238445abaac7ca6
Reviewed-on: https://go-review.googlesource.com/c/go/+/182557
Run-TryBot: Agniva De Sarker <a5f0d8ec472f89aaf942c60f780953deb78cdfb5@gmail.com>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Richard Musiol <eb533a4b7e679e5143b37a0022300174aaa46b21@gmail.com>
Reviewed-by: Cherry Zhang <d62e63aa42ce272d7b6a5055d97e942b33a34679@google.com>

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