ARM: Implement native substring copying.

src/arm/simulator-arm.cc

 // Copyright 2010 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 1767 matching lines @@
     default: {
       UNREACHABLE();
       break;
     }
   }
   if (instr->HasB()) {
     if (instr->HasL()) {
       uint8_t byte = ReadB(addr);
       set_register(rd, byte);
     } else {
-      UNIMPLEMENTED();
+      uint8_t byte = get_register(rd);
+      WriteB(addr, byte);
     }
   } else {
     if (instr->HasL()) {
       set_register(rd, ReadW(addr, instr));
     } else {
       WriteW(addr, get_register(rd), instr);
     }
   }
 }
 
@@ skipping 487 matching lines @@
   uintptr_t* stack_slot = reinterpret_cast<uintptr_t*>(current_sp);
   uintptr_t address = *stack_slot;
   set_register(sp, current_sp + sizeof(uintptr_t));
   return address;
 }
 
 
 } }  // namespace assembler::arm
 
 #endif  // !defined(__arm__)