Fix error: implicit conversion loses integer precision

http://ci.rvm.jp/results/trunk_clang_50@silicon-docker/627906
```
iseq.h:41:36: error: implicit conversion loses integer precision: 'rb_num_t' (aka 'unsigned long') to 'int' [-Werror,-Wshorten-64-to-32]
    int cnt = iseq->body->variable.flip_count;
        ~~~   ~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~
```

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@62708 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

compile.c

@@ -8751,7 +8751,7 @@ ibf_load_iseq_each(const struct ibf_load *load, rb_iseq_t *iseq, ibf_offset_t of
 
     ISEQ_COVERAGE_SET(iseq, Qnil);
     ISEQ_ORIGINAL_ISEQ_CLEAR(iseq);
-    iseq->body->variable.flip_count = (int)body->variable.flip_count;
+    iseq->body->variable.flip_count = body->variable.flip_count;
 
     {
 	VALUE realpath = Qnil, path = ibf_load_object(load, body->location.pathobj);

iseq.h

@@ -35,10 +35,10 @@ rb_call_info_kw_arg_bytes(int keyword_len)
 
 #define ISEQ_FLIP_CNT(iseq) (iseq)->body->variable.flip_count
 
-static inline int
+static inline rb_snum_t
 ISEQ_FLIP_CNT_INCREMENT(const rb_iseq_t *iseq)
 {
-    int cnt = iseq->body->variable.flip_count;
+    rb_snum_t cnt = iseq->body->variable.flip_count;
     iseq->body->variable.flip_count += 1;
     return cnt;
 }

vm_core.h

@@ -412,7 +412,7 @@ struct rb_iseq_constant_body {
     struct rb_call_cache *cc_entries; /* size is ci_size = ci_kw_size */
 
     struct {
-      rb_num_t flip_count;
+      rb_snum_t flip_count;
       VALUE coverage;
       VALUE original_iseq;
     } variable;