Do not define _WIN32_WINNT multiple times

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@34284 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

ChangeLog

@@ -1,3 +1,9 @@
+Fri Jan 13 03:28:00 2012  Luis Lavena  <luislavena@gmail.com>
+
+	* ext/socket/extconf.rb (if ipv6): only define _WIN32_WINNT if was not
+	  previously defined. This solve warnings with multiple defines in
+	  command line with GCC 4.6.1
+
 Thu Jan 12 18:44:31 2012  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* lib/mkmf.rb: fix r33904 and revert r33905.  initialize global

ext/socket/extconf.rb

@@ -56,7 +56,7 @@ end
 
 if ipv6
   if $mingw
-    $CPPFLAGS << " -D_WIN32_WINNT=0x501"
+    $CPPFLAGS << " -D_WIN32_WINNT=0x501" unless $CPPFLAGS.include?("_WIN32_WINNT")
   end
   ipv6lib = nil
   class << (fmt = "unknown")