compile.c: not simple if keyword args

* compile.c (iseq_set_arguments): not a simple single argument if any
  keyword arguments exist.  [ruby-core:55203] [Bug #8463]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@41021 b2dd03c8-39d4-4d8f-98ff-823fe69b080e