* template/known_errors.inc.tmpl: generate defined_error() and
  undefined_error() instead of set_syserr.

* error.c (Init_syserr): define defined_error() and undefined_error()
  to follow the above change.
  (rb_strerrno): defined.

* thread_pthread.c: show error message and errno macro name with
  rb_bug.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@25893 b2dd03c8-39d4-4d8f-98ff-823fe69b080e