* io.c, internal.h (rb_io_flush_raw): new function to select calling
  fsync() (on Windows).

* io.c (rb_io_flush_raw): use above function.

* file.c (rb_file_truncate): use above function.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@42564 b2dd03c8-39d4-4d8f-98ff-823fe69b080e