ext_conf_builder.rb: clear DESTDIR

* lib/rubygems/ext/ext_conf_builder.rb (Gem::Ext::ExtConfBuilder.build):
  clear DESTDIR so RUBYARCHDIR and RUBYLIBDIR are not be overrdden.
  [Bug #7698]


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@39590 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
* 2013-03-05

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@39591 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
ext_conf_builder.rb: clear DESTDIR

* lib/rubygems/ext/ext_conf_builder.rb (Gem::Ext::ExtConfBuilder.build):
  clear DESTDIR so RUBYARCHDIR and RUBYLIBDIR are not be overrdden.
  [Bug #7698]


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@39592 b2dd03c8-39d4-4d8f-98ff-823fe69b080e