file.c: fsid_t may not be defined

* configure.in: check if fsid_t is defined.

* file.c (statfs_fsid): fsid_t may not be defined, assume long in
  that case.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@45678 b2dd03c8-39d4-4d8f-98ff-823fe69b080e