Add rake task to compile without C23 extensions

Author: soutaro

Rakefile

@@ -437,3 +437,11 @@ task :changelog do
     puts "  (🤑 There is no *unreleased* pull request associated to the milestone.)"
   end
 end
+
+desc "Compile extension without C23 extensions"
+task :compile_c99 do
+  ENV["TEST_NO_C23"] = "true"
+  Rake::Task[:"compile"].invoke
+ensure
+  ENV.delete("TEST_NO_C23")
+end

ext/rbs_extension/extconf.rb

@@ -13,5 +13,9 @@
 
 append_cflags ['-std=gnu99', '-Wimplicit-fallthrough', '-Wunused-result']
 append_cflags ['-O0', '-g'] if ENV['DEBUG']
+if ENV["TEST_NO_C23"]
+  puts "Adding -Wc2x-extensions to CFLAGS"
+  $CFLAGS << " -Werror -Wc2x-extensions"
+end
 
 create_makefile 'rbs_extension'