sitelibdir makes no sense in ruby itself

spec/default.mspec

@@ -7,6 +7,8 @@ require "./rbconfig" unless defined?(RbConfig)
 load File.dirname(__FILE__) + '/ruby/default.mspec'
 OBJDIR = File.expand_path("spec/ruby/optional/capi/ext")
 class MSpecScript
+  @testing_ruby = true
+
   builddir = Dir.pwd
   srcdir = ENV['SRCDIR']
   srcdir ||= File.read("Makefile", encoding: "US-ASCII")[/^\s*srcdir\s*=\s*(.+)/i, 1] rescue nil

spec/ruby/language/predefined_spec.rb

@@ -854,6 +854,8 @@ describe "Execution variable $:" do
   end
 
   it "default $LOAD_PATH entries until sitelibdir included have @gem_prelude_index set" do
+    skip "no sense in ruby itself" if MSpecScript.instance_variable_defined?(:@testing_ruby)
+
     $:.should.include?(RbConfig::CONFIG['sitelibdir'])
     idx = $:.index(RbConfig::CONFIG['sitelibdir'])