Ruby

• io.c (rb_f_syscall): Some syscall return unsigned or pointer value.
  Therefore we should only check the result is -1 or not. [ruby-core:34062]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@30526 b2dd03c8-39d4-4d8f-98ff-823fe69b080e