* ext/etc/etc.c: Etc.uname method implemented.

* ext/etc/extconf.rb: Check uname() function.

  [ruby-core:62139] [Feature #9770]



git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@45983 b2dd03c8-39d4-4d8f-98ff-823fe69b080e