Set up call to 'rake cross native gem' as the main build step now.
This utilizes the 'cross compile' feature where we can build multiple versions of ruby under one gem package, though it's really going to be used for 'direct compilation'. The following variables need to be set to run the tools/build_p4ruby.sh now:
* RUBY_USE_VERSION - Should be the rvm version with the gem for publishing to geminabox
* RUBY_CC_VERSION - The colon (:) delimited string of ruby versions to build - each version should be installed via RVM and registered in ~/.rake_compiler/config.yml
* P4RUBY_CROSS_PLATFORM - The platform ID we are building on, needs to be set, e.g., 'x86_64-linux', 'i686-linux', 'x86_64-darwin-11'. Note that OS X uses the darwin 'version'.