cmd/compile: ensure equal functions don't do unaligned loads

On architectures which don't support unaligned loads, make sure we
don't generate code that requires them.

Generated hash functions also matter in this respect, but they all look ok.

Update #37716
Fixes #46283

Change-Id: I6197fdfe04da4428092c99bd871d93738789e16b
Reviewed-on: https://go-review.googlesource.com/c/go/+/322151


Trust: Keith Randall <khr@golang.org>
Trust: Josh Bleecher Snyder <josharian@gmail.com>
Run-TryBot: Keith Randall <khr@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>
Reviewed-by: eric fang <eric.fang@arm.com>
TryBot-Result: Go Bot <gobot@golang.org>