cmd/compile: add memory argument to GetCallerSP

cmd/compile: add memory argument to GetCallerSP

We need to make sure that when we get the stack pointer, we get it
at the right time.

V = GetCallerSP
Call()
W = GetCallerSP

If Call causes a stack growth, then we will be in a situation
where V != W. So it matters when GetCallerSP operations get scheduled.
Add a memory argument to GetCallerSP so it can't be reordered with
things like calls.

Change-Id: I6cc801134c38e358c5a1ec0c09d38379a16a4184
Reviewed-on: https://go-review.googlesource.com/c/go/+/453515
Reviewed-by: Martin Möhrmann <moehrmann@google.com>
Run-TryBot: Keith Randall <khr@golang.org>
Reviewed-by: Martin Möhrmann <martin@golang.org>
Reviewed-by: Robert Griesemer <gri@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>