Ruby

json/parser/prereq.mk: use enum

• ext/json/parser/prereq.mk (parser.c): use enum instead of
  static const int to get rid of unused-const-variable warnings.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@45356 b2dd03c8-39d4-4d8f-98ff-823fe69b080e