win32/resolv: fix for cygwin

* ext/win32/resolv/resolv.c: needs windows.h for iphlpapi.h on
  cygwin.  [ruby-core:76791] [Bug #12663]
* ext/win32/resolv/resolv.c (w32error_make_error): use
  Win32::Resolv::Error, an alias of Win32::Registry::Error.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@55849 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

ChangeLog

@@ -1,3 +1,11 @@
+Wed Aug 10 15:35:03 2016  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* ext/win32/resolv/resolv.c: needs windows.h for iphlpapi.h on
+	  cygwin.  [ruby-core:76791] [Bug #12663]
+
+	* ext/win32/resolv/resolv.c (w32error_make_error): use
+	  Win32::Resolv::Error, an alias of Win32::Registry::Error.
+
 Tue Aug  9 17:50:00 2016  Kenta Murata  <mrkn@mrkn.jp>
 
 	* hash.c (rb_hash_map_v, rb_hash_map_v_bang): impelement Hash#map_v and

ext/win32/lib/win32/resolv.rb

@@ -9,6 +9,7 @@ require 'win32/registry'
 module Win32
   module Resolv
     API = Registry::API
+    Error = Registry::Error
 
     def self.get_hosts_path
       path = get_hosts_dir

ext/win32/resolv/extconf.rb

@@ -1 +1,3 @@
-create_makefile('win32/resolv')
+if have_library('iphlpapi', 'GetNetworkParams')
+  create_makefile('win32/resolv')
+end