Invalid rubysitedir value if ruby is compiled without sitedir

If ruby is compiled with --with-sitedir=no, RbConfig::CONFIG['sitelibdir'] will report something like $(sitedir)/2.7.0 which is an invalid value. The RbConfig value is used by Facter to fill the ruby.sitedir/rubysitedir fact. Facter should not report the fact at all in this case.

Actual output:

[root@heroic-bugle ~]# facter ruby

{

  platform => "x86_64-linux",

  sitedir => "$(sitedir)/2.7.0",

  version => "2.7.3"

}

Expected output:

[root@heroic-bugle ~]# facter ruby

{

  platform => "x86_64-linux",

  version => "2.7.3"

}