runtime: account for spill slots in Windows callback compilation

The Go ABI, as it stands, requires spill space to be reserved for
register arguments. syscall.NewCallback (because of compileCallback)
does not actually reserve this space, leading to issues if the Go code
it invokes actually makes use of it.

Fixes #46301.

Change-Id: Idbc3578accaaaa29e4ba32291ef08d464da0b7b0
Reviewed-on: https://go-review.googlesource.com/c/go/+/322029


Trust: Michael Knyszek <mknyszek@google.com>
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Egon Elbre <egonelbre@gmail.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>