Skip clock_getres spec on BSD
Skip clock_getres spec on BSD

* clock_getres() seems to be incorrect on BSD:
  https://rubyci.org/logs/rubyci.s3.amazonaws.com/freebsd11zfs/ruby-trunk/log/20190427T183003Z.fail.html.gz

eregon/rubyspec,eregon/rubyspec,ruby/spec,nobu/rubyspec,ruby/spec,eregon/rubyspec,nobu/rubyspec,ruby/spec,nobu/rubyspec