reuse cc->call

I noticed that in case of cache misshit, re-calculated cc->me can
be the same method entry than the pevious one.  That is an okay
situation but can't we partially reuse the cache, because cc->call
should still be valid then?

One thing that has to be special-cased is when the method entry
gets amended by some refinements.  That happens behind-the-scene
of call cache mechanism.  We have to check if cc->me->def points to
the previously saved one.

Calculating -------------------------------------
                          trunk        ours
vm2_poly_same_method     1.534M      2.025M i/s -      6.000M times in 3.910203s 2.962752s

Comparison:
             vm2_poly_same_method
                ours:   2025143.9 i/s
               trunk:   1534447.2 i/s - 1.32x  slower

1 files changed, 1 insertions, 1 deletions

diff --git a/insns.def b/insns.def
index e3edc5e29f..f365106e2c 100644
--- a/insns.def
+++ b/insns.def
@@ -911,7 +911,7 @@ invokeblock
 // attr rb_snum_t sp_inc = sp_inc_of_invokeblock(ci);
 {
     static struct rb_call_cache cc = {
-        0, 0, NULL, vm_invokeblock_i,
+        0, 0, NULL, NULL, vm_invokeblock_i,
     };
 
     VALUE bh = VM_BLOCK_HANDLER_NONE;