Add MRB_SET_INSTANCE_TT to enable mrb_mutex_data_free to be called on GC. @matsumoto-r: Thank you for your advice!
Add MRB_SET_INSTANCE_TT to enable mrb_mutex_data_free to be called on GC.
@matsumoto-r: Thank you for your advice!

matsumoto-r/mruby-mutex,matsumoto-r/mruby-mutex