Since #6945 the extension dir changed to Gem::BasicSpecification's implementation, we didn't hook that in rubygems_ext.rb. So for universal rubies, we ended up using the universal platform name when installing, but arch replaced platform name when checking. This lead to native extensions can never be correctly installed on universal rubies.

Hook Gem::BasicSpecifications so the behavior is consistent on installing and checking.

https://github.com/rubygems/rubygems/commit/8d699ed096