configure.in: no visibility option for older GCC
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@37296 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
configure.in: no visibility option for older GCC
available before GCC 4, so do not use -fvisibility option in that
case. [ruby-core:48147] [Bug #7205]
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@37296 b2dd03c8-39d4-4d8f-98ff-823fe69b080e