* file.c (rb_io_statfs): need to define even if the system doesn't have
  fstatfs(2).

* test/ruby/test_file.rb (TestFile#test_statfs): skip if IO#stafs is not
  implemented.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@45668 b2dd03c8-39d4-4d8f-98ff-823fe69b080e