* lib/mkmf.rb (MakeMakefile#create_makefile): output new macro
  disthdrdir to specify the path of id.h, parse.h and etc.

* ext/ripper/depend: use above macro.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@40278 b2dd03c8-39d4-4d8f-98ff-823fe69b080e