Fix NaN pack specs
Fix NaN pack specs

* The specific value varies between MRI versions, even on the same
  OS and architecture, so allow both.
* platform_is "86" was never executed before the fix in MSpec.
  https://github.com/ruby/mspec/commit/231e2cee

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