runtime,runtime/cgo: save all necessary registers on entry to Go on Windows

There are several assembly functions that transition from the Windows
ABI to the Go ABI. These all need to save all registers that are
callee-save in the Windows ABI and caller-save in the Go ABI and
prepare the register state for Go. However, they all do this slightly
differently and most of them don't save the necessary XMM registers
for this transition (which could corrupt them in the C caller).
Furthermore, now that we have a carefully specified Go ABI, it's clear
that none of these actually get all of the details 100% right.

So, unify this code into two macros in a shared header in
runtime/cgo/abi_amd64.h that handle all necessary registers and setup
and use these macros everywhere on Windows that handles transitions
from C to Go.

Change-Id: I62f41345a507aad1ca383814ac8b7e2a9ffb821e
Reviewed-on: https://go-review.googlesource.com/c/go/+/309769
Trust: Austin Clements <austin@google.com>
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>

src/cmd/internal/obj/x86/obj6.go

@@ -912,7 +912,7 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
 		}
 
 		if autoffset != deltasp {
-			ctxt.Diag("unbalanced PUSH/POP")
+			ctxt.Diag("%s: unbalanced PUSH/POP", cursym)
 		}
 
 		if autoffset != 0 {