configure.in: RUNRUBY_COMMAND

* configure.in, Makefile.in (RUNRUBY_COMMAND): separate from RUNRUBY,
  to use options for runruby.rb.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43093 b2dd03c8-39d4-4d8f-98ff-823fe69b080e