* common.mk (ext/ripper/ripper.c): id.h in VPATH may exist in the build
  directory.

* common.mk (ext/ripper/ripper.c): $(RM) was not defined.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@48522 b2dd03c8-39d4-4d8f-98ff-823fe69b080e