runtime: really pass return value to Windows in externalthreadhandler

When Windows calls externalthreadhandler it expects to receive
return value in AX. We don't set AX anywhere. Change that.
Store ctrlhandler1 and profileloop1 return values into AX before
returning from externalthreadhandler.

Fixes #10215.

Change-Id: Ied04542cc3ebe7d4a26660e970f9f78098143591
Reviewed-on: https://go-review.googlesource.com/8901Reviewed-by: Minux Ma <minux@golang.org>
Run-TryBot: Alex Brainman <alex.brainman@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/os/signal/signal_windows_test.go

@@ -10,7 +10,6 @@ import (
 	"os"
 	"os/exec"
 	"path/filepath"
-	"runtime"
 	"syscall"
 	"testing"
 	"time"
@@ -32,9 +31,6 @@ func sendCtrlBreak(t *testing.T, pid int) {
 }
 
 func TestCtrlBreak(t *testing.T) {
-	if runtime.GOARCH == "386" {
-		t.Skip("known failing test on windows/386, see https://golang.org/issue/10215")
-	}
 	// create source file
 	const source = `
 package main

src/runtime/os1_windows.go

@@ -492,7 +492,7 @@ func profilem(mp *m) {
 	sigprof(r.ip(), r.sp(), 0, gp, mp)
 }
 
-func profileloop1() {
+func profileloop1(param uintptr) uint32 {
 	stdcall2(_SetThreadPriority, currentThread, _THREAD_PRIORITY_HIGHEST)
 
 	for {

src/runtime/sys_windows_386.s

@@ -213,9 +213,11 @@ TEXT runtime·externalthreadhandler(SB),NOSPLIT,$0
 	MOVL	CX, g_stackguard1(SP)
 	MOVL	DX, (g_stack+stack_hi)(SP)
 
+	PUSHL	AX			// room for return value
 	PUSHL	16(BP)			// arg for handler
 	CALL	8(BP)
 	POPL	CX
+	POPL	AX			// pass return value to Windows in AX
 
 	get_tls(CX)
 	MOVL	g(CX), CX

src/runtime/sys_windows_amd64.s

@@ -250,9 +250,11 @@ TEXT runtime·externalthreadhandler(SB),NOSPLIT,$0
 	MOVQ	CX, g_stackguard1(SP)
 	MOVQ	DX, (g_stack+stack_hi)(SP)
 
+	PUSHQ	AX			// room for return value
 	PUSHQ	32(BP)			// arg for handler
 	CALL	16(BP)
 	POPQ	CX
+	POPQ	AX			// pass return value to Windows in AX
 
 	get_tls(CX)
 	MOVQ	g(CX), CX