`vm_opt_method_table` is me=>bop table to manage the optimized
methods (by specialized instruction). However, `me` can be invalidated
to invalidate the method cache entry.
[Bug #17725]
To solve the issue, use `me-def` instead of `me` which simply copied
at invalidation timing.
A test by @jeremyevans https://github.com/ruby/ruby/pull/4376