[dev.simd] cmd/compile: tweak sort order in generator

This CL is created by simdgen CL 684056

Change-Id: Ie4240098bbe701531ab82d5200e92857726f1ba7
Reviewed-on: https://go-review.googlesource.com/c/go/+/684076
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>

Author: dr2chase