cmd/compile: align stack-allocated backing stores higher than required
Because that's what mallocgc did and some user code came to rely on it.
Fixes #73199
Change-Id: I45ca00d2ea448e6729ef9ac4cec3c1eb0ceccc89
Reviewed-on: https://go-review.googlesource.com/c/go/+/666116 Reviewed-by: t hepudds <thepudds1460@gmail.com> Reviewed-by: Keith Randall <khr@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Keith Randall <khr@golang.org> Reviewed-by: Cherry Mui <cherryyz@google.com>