* configure.in, ext/socket/extconf.rb: test netinet/in_systm.h in
  ext/socket/extconf.rb instead of configure.in.

  Originally, netinet/in_systm.h is included for NextStep, OpenStep,
  and Rhapsody.  [ruby-core:1596]



git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@39263 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
* ext/socket/extconf.rb: reorder header tests to consider inclusion
  order in rubysocket.h.



git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@39264 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
* ext/socket/extconf.rb: don't test sys/feature_tests.h which is not
  used now.
  It was included in r7901 as "bug of gcc 3.0 on Solaris 8 ?".



git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@39265 b2dd03c8-39d4-4d8f-98ff-823fe69b080e