mkmf/base.rb: capture output

* test/mkmf/base.rb (TestMkmf::Base::Capture#write): capture
  output inside mkmf method.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@52438 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

test/mkmf/base.rb

@@ -49,7 +49,11 @@ module TestMkmf::Base
       @filter = block
     end
     def write(s)
-      @buffer << s if @out
+      if @out
+        @buffer << s
+      elsif @origin
+        @origin << s
+      end
     end
   end