gem install mysql2 Building native extensions. This could take a while... ERROR: Error installing mysql2: ERROR: Failed to build gem native extension. /Users/frank/.rbenv/versions/2.2.4/bin/ruby -r ./siteconf20161017-40878-1pj8mbn.rb extconf.rb checking for ruby/thread.h... yes checking for rb_thread_call_without_gvl() in ruby/thread.h... yes checking for rb_thread_blocking_region()... no checking
