Workaround issue with $LOAD_PATH / RbConfig::CONFIG['sitelibdir'] on Windows

* See ruby/setup-ruby#762 (comment)

Author: eregon

language/predefined_spec.rb

@@ -1075,8 +1075,14 @@ def obj.foo2; yield; 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'])
+    if platform_is :windows
+      # See https://github.com/ruby/setup-ruby/pull/762#issuecomment-2917460440
+      $:.should.include? { |e| File.realdirpath(e) == RbConfig::CONFIG['sitelibdir'] }
+      idx = $:.index { |e| File.realdirpath(e) == RbConfig::CONFIG['sitelibdir'] }
+    else
+      $:.should.include?(RbConfig::CONFIG['sitelibdir'])
+      idx = $:.index(RbConfig::CONFIG['sitelibdir'])
+    end
 
     $:[idx..-1].all? { |p| p.instance_variable_defined?(:@gem_prelude_index) }.should be_true
     $:[0...idx].all? { |p| !p.instance_variable_defined?(:@gem_prelude_index) }.should be_true