windows: port to ARM64

This also fixes up some spaces->tabs issues and moves build tags from
the file contents to the file name.

Updates golang/go#36439.

Change-Id: Iafa03e26575603a802832e587bb18ebd16fd176b
Reviewed-on: https://go-review.googlesource.com/c/sys/+/289449
Trust: Jason A. Donenfeld <Jason@zx2c4.com>
Trust: Alex Brainman <alex.brainman@gmail.com>
Run-TryBot: Jason A. Donenfeld <Jason@zx2c4.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Alex Brainman <alex.brainman@gmail.com>
Reviewed-by: Russ Cox <rsc@golang.org>

windows/svc/sys_windows_amd64.s

@@ -0,0 +1,46 @@
+// Copyright 2012 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// func servicemain(argc uint32, argv **uint16)
+TEXT ·servicemain(SB),7,$0
+	MOVQ	SP, AX
+	ANDQ	$~15, SP	// alignment as per Windows requirement
+	SUBQ	$48, SP		// room for SP and 4 args as per Windows requirement
+				// plus one extra word to keep stack 16 bytes aligned
+	MOVQ	AX, 32(SP)
+
+	MOVL	CX, ·sArgc(SB)
+	MOVQ	DX, ·sArgv(SB)
+
+	MOVQ	·sName(SB), CX
+	MOVQ	$·servicectlhandler(SB), DX
+	// BUG(pastarmovj): Figure out a way to pass in context in R8.
+	// Set context to 123456 to test issue #25660.
+	MOVQ	$123456, R8
+	MOVQ	·cRegisterServiceCtrlHandlerExW(SB), AX
+	CALL	AX
+	CMPQ	AX, $0
+	JE	exit
+	MOVQ	AX, ·ssHandle(SB)
+
+	MOVQ	·goWaitsH(SB), CX
+	MOVQ	·cSetEvent(SB), AX
+	CALL	AX
+
+	MOVQ	·cWaitsH(SB), CX
+	MOVQ	$4294967295, DX
+	MOVQ	·cWaitForSingleObject(SB), AX
+	CALL	AX
+
+exit:
+	MOVQ	32(SP), SP
+	RET
+
+// I do not know why, but this seems to be the only way to call
+// ctlHandlerProc on Windows 7.
+
+// func ·servicectlhandler(ctl uint32, evtype uint32, evdata uintptr, context uintptr) uintptr {
+TEXT ·servicectlhandler(SB),7,$0
+	MOVQ	·ctlHandlerExProc(SB), AX
+	JMP	AX