* configure.in (rb_cv_gnu_qsort_r): use compile error "conflicting
  types for 'qsort_r'" instead of AC_RUN_IFELSE.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@44894 b2dd03c8-39d4-4d8f-98ff-823fe69b080e