Showing all a Gem's build flags

Question

This is more a curiosity than necessity question. I've just installed nokogiri again with RubyGems and it is saying "WARNING: Nokogiri was built against LibXML version 2.7.5, but has dynamically loaded 2.7.6" This is easy enough to fix, but it lead to a more general question: how do I see all the configuration options for a rubygem before installing it?

I found the easiest way I know how is to visit the gem folder an run "ruby nokogiri-0.0.0/ext/nokogiri/extconf.rb -h" and that shows me it, but there has to be an easier way, right?

I was expecting some kind of "sudo gem install nokogiri -- --help" command that would show the build flags. I've searched around a bit but didn't see anything, anybody know how to do this before I go digging into RG's source :)?