extmk.rb: do not exclude readline

* ext/extmk.rb: do not exclude readline by default on win32.  it
  would not be completely impossible.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@49212 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

ext/extmk.rb

@@ -496,7 +496,7 @@ ext_prefix = "#{$top_srcdir}/ext"
 exts = $static_ext.sort_by {|t, i| i}.collect {|t, i| t}
 default_exclude_exts =
   if $mswin or $mingw
-    %w'pty readline syslog'
+    %w'pty syslog'
   else
     %w'*win32*'
   end