Skip debase extconf.rb on non-CRuby

[eregon]

Related: ruby-debug/ruby-debug-ide#240

[eregon]

Ping, I'd like to merge this.

[hurricup]

This backend is not supposed to run with truffleruby

[eregon]

Yes, that's why this code is skipping it.
It's still valuable that the gem installs, otherwise e.g. ruby-debug-ide cannot be installed either and it leads to more workarounds in Gemfiles (and it's not always possible, e.g., if a gem depends on ruby-debug-ide and that gem is in the Gemfile, and it cannot be skipped because it has other dependencies, which we found in some apps).

[eregon]

If the changes in this file are problematic, I can remove them or redo them differently.
The most critical part is that the debase C extensions are not attempted to be compiled on non-CRuby (because that would just fail).

[eregon]

@hurricup Could you merge this?
See for instance oracle/truffleruby#3359, that needs both ruby-debug-ide and debase to no-op on TruffleRuby and other non-CRuby.

[hurricup]

I'm sorry, I still don't understand what are you trying to achieve? This gem is not intended to be used with truffleruby as well as ruby-debug-ide.

[eregon]

what are you trying to achieve?

To let the gem install fine on truffleruby, so there is no need to tweak the Gemfile.
In some cases it is (AFAIK) not possible to tweak the Gemfile, we had such a case internally at Oracle:
Suppose there is a gem my-dev-tools that depend on ruby-debug-ide (but not only, also other gems which do work on truffleruby) and that's part of the Gemfile.
There is no solution there, because removing my-dev-tools would remove too much and break the app/tests.
Using something like gem 'debase', platforms: :mri does not work.
The only solution is to let ruby-debug-ide (and its dependencies as known by RubyGems, so that's debase) install fine on TruffleRuby and noop at runtime.

It's a fairly common practice to let gems install on TruffleRuby/JRuby/etc even when they are not supported, so at least they don't break bundle install. Some examples are stackprof, bootsnap, etc.

[eregon]

The reason for this is explained in the commit message: 06bdb3c

But maybe it's the wrong place to do this and instead we should change lib/ruby-debug-ide.rb to noop earlier.