from https://github.com/rubygems/rubygems/commit/bfb0ae69776069155d2092702bfbb5a12617d85a

  Pick from https://github.com/rubygems/rubygems/commit/dfbb5a38114640e0d8d616861607f3de73ee0199

Signed-off-by: Takuya Noguchi <takninnovationresearch@gmail.com>

Running a command like that is actually removing any previous default
bundler specs in the default RubyGems installation (outside of destdir).
It should instead only modify destdir.

https://github.com/rubygems/rubygems/commit/5ed275383c

https://github.com/rubygems/rubygems/commit/16d01f9486

Since a few commits ago, we no longer call `Gem::Specification.reset`
after each invocation of `Gem::Installer#install`. This means we don't
call it when the default Bundler is installed during `gem update
--system`. This causes no issues until the end of the upgrade process
when:

* The previous default Bundler spec is removed from disk.
* All specification stubs are turned into real specifications by loading
  them from disk. But the one for Bundler no longer exists so
  materializes to `nil` and regenerating binstubs crashes like this:

  ```
  Bundler 2.4.0.dev installed
  RubyGems 3.4.0.dev installed
  Regenerating binstubs
  ERROR:  While executing gem ... (NoMethodError)
      undefined method `platform' for nil:NilClass
    /Users/deivid/Code/rubygems/rubygems/lib/rubygems/commands/pristine_command.rb:116:in `block in execute'
    /Users/deivid/Code/rubygems/rubygems/lib/rubygems/specification.rb:981:in `block in each'
    /Users/deivid/Code/rubygems/rubygems/lib/rubygems/specification.rb:980:in `each'
    /Users/deivid/Code/rubygems/rubygems/lib/rubygems/specification.rb:980:in `each'
    /Users/deivid/Code/rubygems/rubygems/lib/rubygems/commands/pristine_command.rb:116:in `map'
    /Users/deivid/Code/rubygems/rubygems/lib/rubygems/commands/pristine_command.rb:116:in `each'
    /Users/deivid/Code/rubygems/rubygems/lib/rubygems/commands/pristine_command.rb:116:in `select'
    /Users/deivid/Code/rubygems/rubygems/lib/rubygems/commands/pristine_command.rb:116:in `execute'
    /Users/deivid/Code/rubygems/rubygems/lib/rubygems/command.rb:323:in `invoke_with_build_args'
    /Users/deivid/Code/rubygems/rubygems/lib/rubygems/command.rb:301:in `invoke'
    /Users/deivid/Code/rubygems/rubygems/lib/rubygems/commands/setup_command.rb:604:in `regenerate_binstubs'
    /Users/deivid/Code/rubygems/rubygems/lib/rubygems/commands/setup_command.rb:183:in `execute'
    /Users/deivid/Code/rubygems/rubygems/lib/rubygems/command.rb:323:in `invoke_with_build_args'
    /Users/deivid/Code/rubygems/rubygems/lib/rubygems/command_manager.rb:185:in `process_args'
    /Users/deivid/Code/rubygems/rubygems/lib/rubygems/command_manager.rb:149:in `run'
    /Users/deivid/Code/rubygems/rubygems/lib/rubygems/gem_runner.rb:51:in `run'
  setup.rb:33:in `<main>'
  ```

We fix it by more carefully managing the removal of the previous default
Bundler gem.

https://github.com/rubygems/rubygems/commit/9989f6d5af

  https://github.com/rubygems/rubygems/commit/125415593ead9ab69a9f0bb5392c9d7ec61b1f51