cmd/splitdwarf: fix skip on Windows

Unify the two files rather than have to maintain two copies of the
+build line.

Fixes golang/go#32212

Change-Id: I1f9ee4956183aa6248a5a2e83b5760d02532bacb
Reviewed-on: https://go-review.googlesource.com/c/tools/+/178699
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>

cmd/splitdwarf/doc.go

@@ -1,19 +0,0 @@
-// Copyright 2018 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.
-
-/*
-
-Splitdwarf uncompresses and copies the DWARF segment of a Mach-O
-executable into the "dSYM" file expected by lldb and ports of gdb
-on OSX.
-
-Usage: splitdwarf osxMachoFile [ osxDsymFile ]
-
-Unless a dSYM file name is provided on the command line,
-splitdwarf will place it where the OSX tools expect it, in
-"<osxMachoFile>.dSYM/Contents/Resources/DWARF/<osxMachoFile>",
-creating directories as necessary.
-
-*/
-package main // import "golang.org/x/tools/cmd/splitdwarf"

cmd/splitdwarf/splitdwarf.go

@@ -4,7 +4,21 @@
 
 // +build !js,!nacl,!plan9,!solaris,!windows
 
-package main
+/*
+
+Splitdwarf uncompresses and copies the DWARF segment of a Mach-O
+executable into the "dSYM" file expected by lldb and ports of gdb
+on OSX.
+
+Usage: splitdwarf osxMachoFile [ osxDsymFile ]
+
+Unless a dSYM file name is provided on the command line,
+splitdwarf will place it where the OSX tools expect it, in
+"<osxMachoFile>.dSYM/Contents/Resources/DWARF/<osxMachoFile>",
+creating directories as necessary.
+
+*/
+package main // import "golang.org/x/tools/cmd/splitdwarf"
 
 import (
 	"crypto/sha256"