* lib/rubygems/ext/builder.rb (Gem::Ext::Builder.make): Pass
  DESTDIR via command line to override what's in MAKEFLAGS.  This
  fixes an installation problem under a package building
  environment where DESTDIR is specified in the (parent) command
  line. [Fixes GH-327]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@41629 b2dd03c8-39d4-4d8f-98ff-823fe69b080e