Fix code for store buffer update on ARM and MIPS (link register was trashed).

runtime/vm/intrinsifier_x64.cc

Index: runtime/vm/intrinsifier_x64.cc
===================================================================
--- runtime/vm/intrinsifier_x64.cc	(revision 24492)
+++ runtime/vm/intrinsifier_x64.cc	(working copy)
@@ -189,7 +189,7 @@
   __ j(ABOVE_EQUAL, &fall_through);
   // Note that RBX is Smi, i.e, times 2.
   ASSERT(kSmiTagShift == 1);
-  // Destroy RCX as we will not continue in the function.
+  // Destroy RCX (ic data) as we will not continue in the function.
   __ StoreIntoObject(RAX,
                      FieldAddress(RAX, RCX, TIMES_4, Array::data_offset()),
                      RDX);