symbol.c: return the results directly

* symbol.c (lookup_str_id, lookup_str_sym, lookup_id_str): return
  the result ID, Symbol, and string directly instead of returning
  via a pointer.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@46971 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
symbol.c: wrap global_symbols tables

* symbol.c (register_symid_direct, unregister_sym): extract to
  wrap global_symbols tables.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@46972 b2dd03c8-39d4-4d8f-98ff-823fe69b080e