extconf.rb: rl_hook_func_t for old readline
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@45240 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
extconf.rb: rl_hook_func_t for old readline
very old readline versions. [ruby-core:61209] [Bug #9578]
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@45240 b2dd03c8-39d4-4d8f-98ff-823fe69b080e