Use stub executables generated by RubyGems istead of original executables.

It resolved the conflict issues when invoking `gem i rdoc` and the binstub
issues with Bundler and Rails.

  [Bug #5060][ruby-core:38257][Fix GH-2023]

  * https://github.com/rubygems/rubygems/pull/2338
  * https://github.com/heroku/heroku-buildpack-ruby/issues/829

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@65963 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

libexec/rdoc

@@ -0,0 +1,44 @@
+#!/usr/bin/env ruby
+#
+#  RDoc: Documentation tool for source code
+#        (see lib/rdoc/rdoc.rb for more information)
+#
+#  Copyright (c) 2003 Dave Thomas
+#  Released under the same terms as Ruby
+
+begin
+  gem 'rdoc'
+rescue NameError => e # --disable-gems
+  raise unless e.name == :gem
+rescue Gem::LoadError
+end
+
+require 'rdoc/rdoc'
+
+begin
+  r = RDoc::RDoc.new
+  r.document ARGV
+rescue Errno::ENOSPC
+  $stderr.puts 'Ran out of space creating documentation'
+  $stderr.puts
+  $stderr.puts 'Please free up some space and try again'
+rescue SystemExit
+  raise
+rescue Exception => e
+  if $DEBUG_RDOC then
+    $stderr.puts e.message
+    $stderr.puts "#{e.backtrace.join "\n\t"}"
+    $stderr.puts
+  elsif Interrupt === e then
+    $stderr.puts
+    $stderr.puts 'Interrupted'
+  else
+    $stderr.puts "uh-oh! RDoc had a problem:"
+    $stderr.puts e.message
+    $stderr.puts
+    $stderr.puts "run with --debug for full backtrace"
+  end
+
+  exit 1
+end
+