I just got a MacBook Pro (my first Mac!) and couldn’t install many gems. All had native dependencies. All failed similarly:
1 $ sudo gem install god
3 Updating metadata for 1 gems from http://gems.rubyforge.org/
6 Building native extensions. This could take a while…
7 ERROR: Error installing god:
8 ERROR: Failed to build gem native extension.
10 /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/bin/ruby extconf.rb install god
11 can’t find header files for ruby.
14 Gem files will remain installed in /Library/Ruby/Gems/1.8/gems/god-0.7.6 for inspection.
15 Results logged to /Library/Ruby/Gems/1.8/gems/god-0.7.6/ext/god/gem_make.out
Hope this helps someone else.