mkmf.rb: fix conflict in have_library
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@54982 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
mkmf.rb: fix conflict in have_library
main(). checking local symbol reference does not make sense.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@54982 b2dd03c8-39d4-4d8f-98ff-823fe69b080e