rb_obj_is_mutex() into include/ruby/intern.h
rb_obj_is_mutex() is currently an internal API function.
However, this function is useful for C extension developers to distinguish between Mutex and other objects extended by Mutex_m.
I want to use it in ext/thread/thread.c for this purpose.
- vm_insnhelper.c (check_match): Fix SEGV with VM_CHECKMATCH_TYPE_CASE
and class of