Displaying All Gem Build Flags

This is more of a curiosity than a matter of necessity. I just installed nokogiri again with RubyGems and it says "WARNING: Nokogiri was built against LibXML version 2.7.5 but loaded dynamically 2.7.6". This is easy enough to fix, but it leads to a more general question: How can I see all the configuration options for rubygem before installing it?

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

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