- ### Problem

  Since https://github.com/ruby/rubygems/pull/9131, we are now
  compiling make rules simultaneously. The number of jobs
  is equal to the number of processors.
  This may be problematic for some users as they want to control
  this value.

  ### Solution

  The number of jobs passed to `make` will now be equal to the
  `BUNDLE_JOBS` value.

  ### Side note

  It's also worth to note that since Bundler installs gems in
  parallel, we may end up running multiple `make -j<JOB>` in parallel
  which would cause exhaust the number of processors we have.
  This problem can be fixed by implementing a GNU jobserver, which I
  plan to do. But I felt that this would be too much change in one PR.

https://github.com/ruby/rubygems/commit/d51995deb9

https://github.com/rubygems/rubygems/commit/b58829a868

https://github.com/rubygems/rubygems/commit/2af1646776

This patch adds `--target-rbconfig` option to specify the rbconfig.rb file
for the deployment target platform. This is useful when cross-compiling
gems. At the moment, this option is only available for `extconf.rb`-based
extensions.

https://github.com/rubygems/rubygems/commit/cf2843f7a2

https://github.com/rubygems/rubygems/commit/e916ccb2d9

https://github.com/rubygems/rubygems/commit/52ae4452c2