Prism-based parser crashes when building ruby/ruby's doc

[st0012]

To reproduce:

// under `build/`
$ export RDOC_USE_PRISM_PARSER=1
$ make html

Generating RDoc HTML files
=========================================================================
RDoc is using the experimental Prism parser to generate the documentation
=========================================================================
Parsing sources...
100% [838/838]  yjit.rb
/Users/hung-wulo/src/github.com/Shopify/ruby/lib/rdoc/code_object/class_module.rb:703:in 'RDoc::ClassModule#superclass': stack level too deep (SystemStackError)
        from /Users/hung-wulo/src/github.com/Shopify/ruby/lib/rdoc/code_object/normal_class.rb:13:in 'RDoc::NormalClass#ancestors'
        from /Users/hung-wulo/src/github.com/Shopify/ruby/lib/rdoc/code_object/normal_class.rb:18:in 'RDoc::NormalClass#ancestors'
        from /Users/hung-wulo/src/github.com/Shopify/ruby/lib/rdoc/code_object/normal_class.rb:18:in 'RDoc::NormalClass#ancestors'
        from /Users/hung-wulo/src/github.com/Shopify/ruby/lib/rdoc/code_object/normal_class.rb:18:in 'RDoc::NormalClass#ancestors'
        from /Users/hung-wulo/src/github.com/Shopify/ruby/lib/rdoc/code_object/normal_class.rb:18:in 'RDoc::NormalClass#ancestors'
        from /Users/hung-wulo/src/github.com/Shopify/ruby/lib/rdoc/code_object/normal_class.rb:18:in 'RDoc::NormalClass#ancestors'