cmd/dist: add windows/arm64 support

- Add Windows SystemInfo constant for arm64
- Add windows/arm64 to GOOS/GOARCH list

This CL is part of a stack adding windows/arm64
support (#36439), intended to land in the Go 1.17 cycle.

Change-Id: I6109bd87512b5cb1d227d7a85fd0ac20eb2259e5
Reviewed-on: https://go-review.googlesource.com/c/go/+/288819
Trust: Russ Cox <rsc@golang.org>
Trust: Jason A. Donenfeld <Jason@zx2c4.com>
Reviewed-by: Alex Brainman <alex.brainman@gmail.com>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/cmd/dist/build.go

@@ -1575,6 +1575,7 @@ var cgoEnabled = map[string]bool{
 	"windows/386":     true,
 	"windows/amd64":   true,
 	"windows/arm":     false,
+	"windows/arm64":   false,
 }
 
 // List of platforms which are supported but not complete yet. These get

src/cmd/dist/sys_windows.go

@@ -29,10 +29,13 @@ type systeminfo struct {
 	wProcessorRevision          uint16
 }
 
+// See https://docs.microsoft.com/en-us/windows/win32/api/sysinfoapi/ns-sysinfoapi-system_info
 const (
 	PROCESSOR_ARCHITECTURE_AMD64 = 9
 	PROCESSOR_ARCHITECTURE_INTEL = 0
 	PROCESSOR_ARCHITECTURE_ARM   = 5
+	PROCESSOR_ARCHITECTURE_ARM64 = 12
+	PROCESSOR_ARCHITECTURE_IA64  = 6
 )
 
 var sysinfo systeminfo
@@ -46,6 +49,8 @@ func sysinit() {
 		gohostarch = "386"
 	case PROCESSOR_ARCHITECTURE_ARM:
 		gohostarch = "arm"
+	case PROCESSOR_ARCHITECTURE_ARM64:
+		gohostarch = "arm64"
 	default:
 		fatalf("unknown processor architecture")
 	}