configure.in: RUBY_RM_RECURSIVE

* configure.in (RUBY_RM_RECURSIVE): this hack is needed by only
  autoconf 2.69 or earlier on darwin.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@40454 b2dd03c8-39d4-4d8f-98ff-823fe69b080e