vm_core.h: flip_cnt in rb_iseq_t

* vm_core.h (rb_iseq_t): move flip_cnt from struct iseq_compile_data,
  because it has same life span as enclosing iseq.  [Bug #7671]
  [ruby-core:51296]


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@38739 b2dd03c8-39d4-4d8f-98ff-823fe69b080e