/usr/lib/ruby/1.8/ is in ruby1.8-dev 1.8.7.352-2ubuntu1.6.
This file is owned by root:root, with mode 0o755.
..
/usr/lib/ruby/1.8/mkmf.rb
/usr/lib/ruby/1.8/x86_64-linux/
/usr/lib/ruby/1.8/x86_64-linux/config.h
/usr/lib/ruby/1.8/x86_64-linux/defines.h
/usr/lib/ruby/1.8/x86_64-linux/digest.h
/usr/lib/ruby/1.8/x86_64-linux/dl.h
/usr/lib/ruby/1.8/x86_64-linux/dlconfig.h
/usr/lib/ruby/1.8/x86_64-linux/dln.h
/usr/lib/ruby/1.8/x86_64-linux/env.h
/usr/lib/ruby/1.8/x86_64-linux/intern.h
/usr/lib/ruby/1.8/x86_64-linux/missing.h
/usr/lib/ruby/1.8/x86_64-linux/node.h
/usr/lib/ruby/1.8/x86_64-linux/re.h
/usr/lib/ruby/1.8/x86_64-linux/regex.h
/usr/lib/ruby/1.8/x86_64-linux/ruby.h
/usr/lib/ruby/1.8/x86_64-linux/rubyio.h
/usr/lib/ruby/1.8/x86_64-linux/rubysig.h
/usr/lib/ruby/1.8/x86_64-linux/st.h
/usr/lib/ruby/1.8/x86_64-linux/util.h
/usr/lib/ruby/1.8/x86_64-linux/version.h