"requiring version.rb" strategy has some issues.

- cannot work when cross-compiling
- often introduces wrong namespace
- must know the superclasses
- costs at each runtime than at build-time

etc.

https://github.com/ruby/actions/runs/500526558?check_suite_focus=true#step:16:127
```
Failures:

  1) Bundler.setup when Bundler is bundled doesn't blow up
     Failure/Error: expect(err).to be_empty

       expected `"fatal: not a git repository (or any of the parent directories): .git\nfatal: not a git repository (o...the parent directories): .git\nfatal: not a git repository (or any of the parent directories): .git".empty?` to return true, got false

       Commands:
       $ /home/runner/work/actions/actions/snapshot-master/ruby \
         -I/home/runner/work/actions/actions/snapshot-master/lib:/home/runner/work/actions/actions/snapshot-master/spec/bundler \
         -rsupport/hax -rsupport/artifice/fail \
         /home/runner/work/actions/actions/snapshot-master/libexec/bundle install --retry 0
       Resolving dependencies...
       Using bundler 2.1.4
       Bundle complete! 1 Gemfile dependency, 1 gem now installed.
       Use `bundle info [gemname]` to see where a bundled gem is installed.
       fatal: not a git repository (or any of the parent directories): .git
       fatal: not a git repository (or any of the parent directories): .git
       fatal: not a git repository (or any of the parent directories): .git
       # $? => 0

       $ /home/runner/work/actions/actions/snapshot-master/ruby \
         -I/home/runner/work/actions/actions/snapshot-master/lib:/home/runner/work/actions/actions/snapshot-master/spec/bundler \
         -rsupport/hax -rsupport/artifice/fail \
         /home/runner/work/actions/actions/snapshot-master/libexec/bundle exec ruby -e \
         require\ \'bundler\'\;\ Bundler.setup
       fatal: not a git repository (or any of the parent directories): .git
       fatal: not a git repository (or any of the parent directories): .git
       fatal: not a git repository (or any of the parent directories): .git
       # $? => 0
     # ./spec/bundler/runtime/setup_spec.rb:1056:in `block (3 levels) in <top (required)>'
     # ./spec/bundler/spec_helper.rb:111:in `block (3 levels) in <top (required)>'
     # ./spec/bundler/spec_helper.rb:111:in `block (2 levels) in <top (required)>'
     # ./spec/bundler/spec_helper.rb:78:in `block (2 levels) in <top (required)>'
make: *** [yes-test-bundler] Error 1
```