86737c50
  3e1aea46

```
$ benchmark-driver -v --rbenv 'before;after;before --jit;after --jit' benchmark/mjit_class.yml --repeat-count=4
before: ruby 2.8.0dev (2020-06-23T07:09:54Z master 37a2e48d) [x86_64-linux]
after: ruby 2.8.0dev (2020-06-23T17:29:56Z inline-class 0ff147c007) [x86_64-linux]
before --jit: ruby 2.8.0dev (2020-06-23T07:09:54Z master 37a2e48d) +JIT [x86_64-linux]
after --jit: ruby 2.8.0dev (2020-06-23T17:29:56Z inline-class 0ff147c007) +JIT [x86_64-linux]
Calculating -------------------------------------
                         before       after  before --jit  after --jit
    mjit_class(self)    39.219M     40.060M       53.502M      69.202M i/s -     40.000M times in 1.019915s 0.998495s 0.747631s 0.578021s
       mjit_class(1)    39.567M     41.242M       52.100M      68.895M i/s -     40.000M times in 1.010935s 0.969885s 0.767749s 0.580591s

Comparison:
                 mjit_class(self)
         after --jit:  69201690.7 i/s
        before --jit:  53502336.4 i/s - 1.29x  slower
               after:  40060289.1 i/s - 1.73x  slower
              before:  39218939.2 i/s - 1.76x  slower

                    mjit_class(1)
         after --jit:  68895358.6 i/s
        before --jit:  52100353.0 i/s - 1.32x  slower
               after:  41241993.6 i/s - 1.67x  slower
              before:  39567314.0 i/s - 1.74x  slower
```

These days I don't use `make benchmark`. The YAML files should be
executable with bare `benchmark-driver` CLI without passing
`RUBYOPT=-Ibenchmark/lib`.

A prerequisite to fix https://bugs.ruby-lang.org/issues/15589 with JIT.
This commit alone doesn't make a significant difference yet, but I thought
this commit should be committed independently.

This method override was discussed in [Misc #16961].

Consider the libraries, which remain exts.mk but not listed in
ext/configure-ext.mk, removed.

This reverts commit 19cabe8b,
which didn't support tool/lib/iseq_loader_checker.rb.

Scripts to run the interpreter via debugger.

Sorted the lines asnd added mjit_build_dir.o dependencies.

`programs` has depended on the "fake" script, which is used by
`test-spec` and etc.

All tests of `test-all` or more require not only the `main` but
also extension libraries.

* Do not chdir in the runner process, to access miniruby.  Chdir
  in worker processes instead.
* GNU make does not export newly added environment variables by
  default, set PARALLEL_TESTS_EXECUTABLE in the runner.

* match uppercase types which would be global, other than [BDT]
* ignore `RUBY_` prefixed symbols

To honor the environment variable, keep GITPULLOPTIONS unset by
default, and appended the option to VCSUP.

At the time of clean-platform, platform directory may not be empty
because of parallel build.

As this rule does not use a separate timestamp file, the target
will be rebuilt every time once it is outdated.

To fix build failures.

This shall fix compile errors.

Fix MSVC build error.

To generate what is necessary via generic_erb.rb instead.

To generate what is necessary via generic_erb.rb instead.