cmd/compile: allow 128-bit values to be spilled

cmd/compile: allow 128-bit values to be spilled

We sometimes use 16-byte load+store to move values around in memory.
In rare circumstances, the loaded value must be spilled because the
store can't happen yet.

In that case, we need to be able to spill the 16-byte value.

Fixes #53454

Change-Id: I09fd08e11a63c6ba3ef781d3f5ede237e9b0132e
Reviewed-on: https://go-review.googlesource.com/c/go/+/413294
Reviewed-by: Keith Randall <khr@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>
Run-TryBot: Keith Randall <khr@golang.org>
Reviewed-by: Keith Randall <khr@google.com>