Make dependency-free gemspec files

The default gems have not been installed yet in the build directory,
bundled gems depending on them can not work.  As those dependencies
should be usable there even without rubygems, make temporary gemspec
files without the dependencies, and use them in the build directory.

ext/extmk.rb

@@ -565,6 +565,17 @@ clean-so::
   end
 }
 
+if @gemname
+  gemdir = File.join($top_srcdir, ext_prefix, @gemname)
+  if File.exist?(spec_file = File.join(gemdir, ".bundled.#{@gemname}.gemspec")) or
+    File.exist?(spec_file = File.join(gemdir, "#{@gemname}.gemspec"))
+    dest = "#{File.dirname(ext_prefix)}/specifications"
+    FileUtils.mkdir_p(dest)
+    File.copy_stream(spec_file, "#{dest}/#{@gemname}.gemspec")
+    puts "copied #{@gemname}.gemspec"
+  end
+end
+
 dir = Dir.pwd
 FileUtils::makedirs(ext_prefix)
 Dir::chdir(ext_prefix)

tool/gem-unpack.rb

@@ -18,5 +18,9 @@ def Gem.unpack(file, dir = nil, spec_dir = nil)
   end
   FileUtils.mkdir_p(spec_dir)
   File.binwrite(File.join(spec_dir, "#{spec.name}-#{spec.version}.gemspec"), spec.to_ruby)
+  unless spec.extensions.empty? or spec.dependencies.empty?
+    spec.dependencies.clear
+  end
+  File.binwrite(File.join(spec_dir, ".bundled.#{spec.name}-#{spec.version}.gemspec"), spec.to_ruby)
   puts "Unpacked #{file}"
 end